Actins are well conserved proteins, showing at least 75% identity in primary sequence between species as divergent as animals, plants, and unicellular organisms. In contrast, recently discovered actin-related proteins demonstrate 35 to 55% identity to conventional actins. At least three different classes of actin-related proteins have been identified; proteins within one class are significantly more similar to each other than to actin or actin-related proteins in another class. To date, three different actin-related proteins have been discovered in C. elegans:
arp-1 ,
arp-2 ,and
arp-3 (for actin related proteins-1, 2, and 3) fall in the three distinct classes, showing ~50%, ~47%, and ~33% identity to actins respectively. These genes were first identified in random cDNA tagging projects (1,2); cDNA sequences were subsequently determined (3).
arp-1 ,shows ~50% homology to C. elegans actins, but is even more similar to human Act-RPV protein (67%). Act-RPV is an integral component of the multi-protein dynactin complex, an activator of cytoplasmic dynein based vesicle transport. Although the C. elegans dynactin complex has not been isolated, homologs of two dynactin complex components, the actin-capping proteins subunits Cap-1 and Cap-2 ,have been identified and characterized (4, 5). Antibodies to C. elegans actin-capping protein recognize transient structures in early C. elegans embryos. The pattern of transient structures suggests a role for actin-capping protein in rotation of the mitotic spindle in the P1 lineage (5, 6, 7). The actin-capping protein in the transient structures may function as a component of a dynactin complex (5). This would suggest co-localization of actin-capping protein and other components of dynactin complex, including that of actin-related protein. We are interested in testing the predicted localization and function of the actin-related protein encoded by
arp-1 .To initiate the analysis of
arp-1 ,we have mapped the gene to right end of chromosome II, right of
unc-52 .PCR assays specific to
arp-1 position the gene near the right ends of the YACs Y53F4 and Y106A11 .In addition, we find that the
arp-1 probe weakly hybridizes to a distinct sequence located on a free contig located near the right end of chromosome III. We have narrowed the location to a region common to YACs Y37D8 ,Y39E4 ,Y106H1 ,and Y107A12 .The location of this sequence is close to but distinct from that of
act-5 (see abstract by Schriefer et al) which also maps to the YAC Y107A12 .We plan to clone both the
arp-1 gene on chromosome II, and the homologous sequence from chromosome III. Interestingly, probes corresponding to the two actin-related genes
arp-2 ,and
arp-3 each also identify two distinct genomic locations, suggesting that C. elegans may contain as many as six arp genes. We plan to (i) examine the expression patterns of
arp-1 and related genes using in-situ hybridizations and/or specific antibodies and (ii) isolate mutations in the gene(s) and examine the effect of the mutation(s) on development of the animal. (l) Waterston R.H. et al, Nature Genetics 1 (1992) 114-123. (2) McCombie W. et al, Nature Genetics 1(1992) 124-131. (3) Lees-Miller, J. and Helfman, D., personal communication. (4) Waddle J. A. et al, Mol. Biol. Cell 4 (1993) 907-917. (5) Waddle, J. A. and Waterston, R.H., Int'l C. elegans meeting, 1993, Abs #2. (6) Hyman A. and White J., J. Cell Biol. 105 (1987) 2123-2135. (7)Hyman A.,J. Cell Biol. 109 (1989)1185-1193