Worm Breeder's Gazette 7(1): 58

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Is unc-92 Actin?

C. Landel, S. Carr, J. Files, D. Hirsh

We thought that unc-92, a dominant unc with disorganized muscle and 
a high reversion frequency, might be an actin gene because of its 
phenotype and because of its map position (Newsletter 6, 23 (1981)).  
Using a Bergerac strain/Bristol strain DNA polymorphism adjacent to 
the cluster of actin genes I, II and III, we were able to locate the 
actin cluster between unc-23 and sma-1.  The arrangement of actin 
genes I, II and III within a 12 kb stretch of DNA suggested mechanisms 
for the high unc-92 reversion frequency, including gene conversion 
between genes and nonhomologous recombination.  Nonhomologous 
recombination should reduce three genes to two which would be easy to 
detect by Southern blot analysis.  We therefore obtained from Bob 
Waterston six revertants of the St15 allele of unc-92; three 
revertants arose spontaneously and three were obtained after an EMS 
mutagenesis.  We isolated DNA from each revertant strain and analyzed 
it by Southern blot analysis.  Five of the revertants showed a pattern 
identical to that of both St15 and N2 when probed for actin sequences, 
but one revertant, RW2246, which derived from the EMS mutagenesis, 
showed an anomalous pattern.  Further restriction mapping of RW2246 by 
Southern blot analysis revealed that this revertant contained a 5kb 
deletion that fused the 5' portion of gene II to the 3' portion of 
gene III.  The fusion could have been the result of recombination 
between genes II and III, deleting the unc-92 lesion and creating a 
new hybrid gene.  We believe that the revertant phenotype resulted 
from this fusion.  Because most of the differences between actin genes 
occur at their 5' ends, the fusion leaves the revertant with the 
equivalent of only genes I and II.  Despite the lack of gene III, the 
revertant appears wild type because genes I and III appear thus far to 
be identical by restriction endonuclease and sequence analyses.  We 
therefore believe that unc-92 is the actin gene cluster, although 
final proof awaits comparison of the actin DNA sequences of N2 and