Worm Breeder's Gazette 11(4): 36

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Molecular Analysis of the emb-5 Locus

Kiyoji Nishiwaki, Tohru Sano and Johji Miwa

Figure 1

emb-5 is a maternally expressed gene and is required for achieving 
the correct timing of E cell division at gastruIation.   The second E 
cell division occurs prematurely at the 26-cell temperature-sensitive 
emb-5 mutants, while in the wiId-type it takes place at the 44-cell 
stage (1, 2).
As previously reported (WBG 11/1:39), we have identified the two 
Tc1s linked to the emb-5 gene in Bergerac BO.  The genomic phage 
clones isolated by Tc1 flanking probes have been assigned on the 
physical map by Drs. J.  Sulston and A.  Coulson and found to be 
separated by about 400 kb.  Based on both genetic and physical map 
data, we estimated that one of the two Tc1s is about 40 kb or one 
cosmid length to the right of emb-5.We have succeeded in transforming 
the ts emb-5 mutant hc61 first by injecting a mixture of three cosmids,
C16B3, C38D4, and W05E6 and then by a single C38D4 cosmid (Figure 1). 
Transformants were usually sick but still produced a few viable 
embryos at nonpermissive temperature.  So far the search for RFLPs in 
emb-5 mutants and putative intragenic revertants of hc61 with C38D4 as 
a probe has not been successful.  Probably, these strains have small 
polymorphisms or point mutations.   There are at least 8 different 
mRNAs transcribed from the C38D4 genomic region.  However, we observed 
no differences in size or amount of any of these transcripts between 
the wild-type and the mutants tested.   We are trying to rescue hc61 
with DNAs subcloned from C38D4 and are also engaged in research to 
identify mutation sites.
[See Figure 1]

Figure 1