Here' some help for any poor devil that will ever have to do a paper on beta actin mrna.. i spent way to much time on this godforsaken project...
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Beta-Actin

The voluntary and involuntary movement of microfilaments and microtubules in the human body is extremely important to the survival of an individual. Without this ability human beings would be unable to defend themselves in dangerous situations, digest nourishment or reproduce, since all of these activities require a type of molecular movement. Actins, which comprise one of the most abundant groups of cellular proteins, play an important part in cellular movement. Other than having a key part in muscle contractions, actins also function in other microfilament-based movements such as internal cell motility. (Wolfe 454)
Actins are the single most abundant cytoplasmic proteins that can be found in both muscle and non-muscle cells of all eukaryotes. Due to the fact that the muscle and non-muscle actins are products of different genes, their properties differ slightly. However, their similar amino acid sequences and shared properties imply that they all evolved from one single ancestral gene. (Baltimore 860)
Actin filaments, which are also called filamentous actin or F actin, can be broken down into globular subunits. These subunits are usually made up of a single polypeptide of molecular weight 41,800 and are known as globular actin or G actin. (Alberts 553)
The usual x-ray and optical diffraction illustrations of actin show that it folds into a complex three-dimensional structure that consists of two lobes that are of unequal size, which are separated by a depression or a cleft on one side. Most actins contain either 374, 375 or 376 amino acids and usually have a total molecular weight near 42,000. There are some unicellular eukaryotes that only have one actin type, but most animals, fungi and plants have two or more distinct actins that are characteristic of muscle and non-muscle cells. The characteristic actins of striated muscle cells are alpha-actins, while the characteristic actins of non-muscle cells are beta and gamma actins. (Wolfe 454)
Even though these actins differ in their function and their properties, they are all very closely related in sequence. When observing the different actin sequences of all eukaryotes they vary by only 15 %, while the actin sequences of animals and some protozoa vary by only 5 %. (Wolfe 455)
Different actins are caused by amino acid substitutions that are confined to limited variable regions in the sequence. All the actins, however, have remaining sequences that are constant. Due to this, when there are substitutions that involve one amino acid being replaced by another, the replacement usually has similar chemical properties like the original. This situation leads scientists to believe that because of the sequence conservation between the different types of actins, most segments of the actin are critical to the function of the protein. Therefore if there were to be any major gene mutations that would substitute amino acids in the segments, this would prove lethal. (Wolfe 455)
Striated, or narrow and parallelly aligned, muscle cells are mostly made up of alpha-actin, which aids in the contraction process. Muscle movement is due to the capability of vertebrate muscular tissue to contract rapidly. These contractions are performed by skeletal muscle, which is made up of long, thin muscle fibers. Each of these fibers is in actuality a single, unusually large cell that was formed by the fusion of many distinct cells. Within the fiber there are long, cylindrical elements called myofibrils, which are the contractile parts of the fiber cell. (Alberts 550)

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The actual myofibrils are made up of alternating assemblies of thick and thin filaments. Thick filaments are made up of myosin molecules, while thin filaments consist of single actin microfilaments in combination with troponin and tropomyosin. (Wolfe 472)
When a muscle fiber contracts, the myosin heads bind to actin. A change occurs which draws the thin filament a short distance past the thick filament. Then the links between the myosin and the actin break and reform farther along the thin filament to repeat the whole process. This process is also called the myosin cross-bridging process. As a result of this, the filaments are pulled past each other in a zipper-like motion, but there is no actual shortening, thickening, or folding of the individual filaments. (Wolfe 466)
Calcium also plays an important part in this cycle. In a resting muscle, there is a Ca + pump that constantly removes Ca from the cytoplasm that surrounds the myofibrils. When an arriving impulse from a motor neuron arrives, the gated Ca+ channels open up, allowing the Ca to diffuse into the thick and thin filaments within the myofibril. There it binds to the troponin of the thin filaments and allows for the whole myosin cross-bridging cycle to occur. When the process is over, then the Ca is driven out of the cytoplasm by the pumps again. (Muscles)
Just as alpha-actins play a very important role in most muscle cells, beta-actin and its mRNA are just as crucial in their non-muscle contemporaries. Beta-actin is mostly present in non-muscle cells, where it functions in an important contractile process that maintains the shape of cells, yet the protein can also be found in some muscle cells. One end of the non-muscle actin filaments is bound to a membrane or to some other attachment site. During experiments when myosin fragments were added to a solution, the negative arrowheads of the actin filament always pointed away from the attachment site, signifying that the filaments had a definite polarity. The other end of the filament, which is positive, pointed towards the membrane. If tension is generated on these filaments due to any kind of interaction with myosin, then a pull on the plasma membrane is exerted, which has the same kind of effect as intercalated disks in smooth muscle tissue. (Baltimore 880)
Initially, scientists believed that it was this interaction between myosin and actin filaments within non-muscle cells that was responsible for non-muscle cell movement. Over time, however, they have come to the conclusion that actin polymerization itself is sufficient enough for most cell movements. This conclusion has been reached due to the results of certain experiments that showed that genetic ablation of several myosins from ameba cell lines failed to inhibit many cell shape changes and certain studies on the intracellular motility of parasites such as Listeria monocytogenes that have failed to identify any roles for myosin in the actual process. (Stossel)
One part of the human body where beta-actin is a key protein is the intestinal tract with its numerous microvilli. Microvilli, which are small projections of the cell membrane that greatly increase the surface area of the cell, such as those of the intestinal epithelial cells, are one of the non-muscle systems in which the beta actin filaments are structured in a well-ordered pattern. Located under the microvilli, there are other networks that are rich in the actin proteins. One of these is the terminal web, which is a
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layer of filaments that crisscross the cytosol just below the microvilli, and the second one is the belt desmosome, which encircles the plasma membrane at the level where it is linked to the plasma membrane. (Baltimore 881)
Within the actual microvilli there is a core of specialized actin filaments that lack myosin and alpha-actin particles but are abundant in beta-actin filaments. These filaments
play an important structural role in maintaining the rigid structure of the microvilli. Other than the beta actin filaments, the microvilli contain other proteins such as fimbrin, villin and fodrin. Fimbrin binds actin filaments in a ratio of 1 fimbrin molecule to 10 actin monomers, causing tightly packed parallel actin bundles to form. Villin, at certain Ca + concentrations, cross-links the actin filaments to form bundles, while fodrin links adjacent actin bundles such as those that encircle the plasma membrane in the region of the belt desosome. (Baltimore 882)
Other than maintaining the structure of the microvilli, beta actin also plays an important part in the process of cytokinesis within non-muscle cells. During the process of cleavage a narrow ring of actin filaments encircles the cleavage furrow and contracts causing the furrow to become narrowed and finally separating the two daughter cells. (Baltimore 884)
Scientists have also been performing experiments with beta-actin mRNA to determine whether or not the beta-actin filaments truly have an impact on cell motility and polarity. During one experiment researchers found that beta-actin mRNA was localized near the leading edge in several cell types. The leading edge was the location where polymerization of actins was actively leading to forward protrusion. Researchers claimed that the location of the beta-actin mRNA was crucial physiologically due to the results of their experiment. In the experiment chicken embryo fibroblasts were treated with antisense oligonucleotides that were complimentary to the localization sequence of the mRNA. This lead to a delocalization of the beta-actin mRNA, an alteration of the actual cell phenotype and a decrease in cell motility. (Condeelis)
After these results the researchers used the Dynamic Image Analysis System to determine the components that were responsible for the change in cell behavior after the mRNA delocalization. Results of the analysis suggested that the net path length and average speed of the anti-sense treated cells were much lower than the normal cells. The total results of the experiment indicated that the delocalization of beta-actin mRNA truly resulted in the delocalization of nucleation sites and the actin protein from the leading edge, which in turn leads to the loss of cell polarity and directional movement. (Condeelis)
Polarity of a cell concerns the presence of distinct front and rear regions within the cell that allow for cellular movement. If cell polarity is lost or exhibited in multiple axes, this may hinder the forward movement of that particular unit. (Wolfe 457)
Another experiment concerned itself with the over-expression of beta-actin and its effects on cell motility. Scientists documented that the over-expression of beta-actin in myoblasts increased cell speed to double that of the control cells. This increase in speed was achieved by an enlargement in the areas of protrusion and retraction and was accompanied by raised levels of beta-actin in those newly protruded regions. These same regions, however, also showed a lowered level of polymerized actins, indicating that the

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rate of protrusion can outpace the rate of actin polymerization in these specific cells. (Peckham)
Lately, researchers have been delving into actin binding proteins (ABP’s), which play an important role in regulating actin filament function and dynamics. The
ABP’s are studied using biochemical, genetic and immunological approaches because their various types allow for numerous methods that can be used to identify their functions and activities. (About Actin)
In general, the study of actins is a pathway worthy of consideration due to the recent discoveries that involve this protein and certain diseases. The actin proteins at the boundary between the cytoskeleton and the plasma membrane control cell shape, define specialized membrane domains and are active in regulating cell-to-cell interactions and adhesions. Within the human erythrocyte, or red blood cell, there are at least 15 different protein species that are involved in its membrane-skeleton. If a mutation in any of these proteins occurs, increase fragility and actual lysis of the cells can arise. Neuromuscular junctions and post-synaptic dendrites in the brain exhibit the same membrane proteins as the erythrocytes, which strongly suggests that the proteins are of overall general importance to cell shape and membrane stability. There even are certain diseases that are linked with actin-associated proteins such as dystrophin, which is an essential component of the sarcolemal membrane. Patients that suffer from genetic mutations that affect dystrophin are afflicted with Duchenne and Becker muscular dystrophy. (About Actin)
As demonstrated in this paper, the actin protein group, which includes beta-actin plays an important role in many different cell functions. Without the presence of the actins in the body, humans would be unable to survive due to the fact that their cells would be incapable of completing certain tasks. Beta-actins are used for the structural support of crucial intestinal microvilli that allow the human intestines to absorb more nutrients by increasing the surface area. They are also present in the plasma membranes of certain non-muscular cells where they promote cell movement with the help of protrusions and retractions. The beta-actins can also affect the polarity of cells, which can cause the individual cells to become incapable of locomotion. Scientists are continuing to study the various actin proteins and they different ways that they impact daily human life. Perhaps one day, more complete understanding of this group of globular proteins will allow doctors to treat some of the more obscure diseases.

Work Cited:
About Actin. Cytoskeleton.com May 8th 2004. http://www.cytoskeleton.com/abactlg.htm

Alberts, Bruce, et al. Molecular Biology of the Cell. New York: Garland Publishing, Inc.
1983.

Baltimore, David and James Darnell and Harvey Lodish, eds. Molecular Cell Biology.
New York: Scientific American Books, Inc. 1990.

Condeelis, J. and Elena Shestakova and R. Singer. The physiological significance of beta
actin mRNA localization in determining cell polarity and directional motility.
Singer Lab Online. May 21st 2004.
http://www.singerlab.org/publications/0105.htm

Muscles. Kimball’s Biology Pages. May 21st 2004.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Muscles.html

Peckham, M. Specific changes to the mechanism of cell locomotion induced by
overexpression of beta-actin. May 8th 2004. National Library of Medicine.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11257002&dopt=Abstract

Stossel, Thomas P. Actin Organization and Remodeling in Cell Structure and Function.
June 21st 2000. May 21st 2004. http://consoude.ujf- grenoble.fr/Cours_Cargese/Cours_Stossel/cours_Stossel.html

Sugiyama, H. et al. Beta-Actin. Invivogen.com May 21st 2004.
http://www.invivogen.com/promdescription/actin-beta.htm

Wolfe, Stephen L. Molecular and Cell Biology. Belmont: Wadsworth Publishing
Company. 1993.

*sighs* its finally done...