Biological Function of Aplysia californica rho Gene
rho genes are a family of genes which are structurally related to the oncogenic ras family. The primary structure of rho genes has been elucidated for the marine snail Aplysia californica, two S. cerevisiae genes, and three human versions, rho A, B and C. They all codify for proteins of an approximate M.W. of 21 kDa (rho-p21) which show 35% homology to the ras proteins. It has been observed that rho proteins are ADP-ribosylated by the botulinum toxin C3 exoenzyme, suggesting that rho proteins could be involved in regulating neuronal function. However very little is known about their actual biological functions. While the human rho A and rho C products have been related to cytoeskeleton organization, the rho A product has a weak transforming activity. We have investigated the biological properties of the Aplysia californica rho-p21 protein when introduced into an heterologous system, and found that it does not induce foci in a regular NIH-3T3 transfection assay. However, the morphology of the cells was slightly altered and cells grew to higher cell densities. Moreover, transforming activity was detected when isolated cell lines were inoculated into nude mice. To further investigate the potential transforming activity of the Aplysia gene, we have also generated a Gly→Val mutation at position 14, equivalent to the activating mutation found in oncogenic ras genes. No apparent increase in the transforming activity was observed, indicating that the effects on growth behaviour are probably not the primary function of rho proteins.
KeywordsHigh Cell Density Transforming Activity Transfected Cell Line Marine Snail Intrinsic GTPase Activity
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