Figure 3.

The putative sns sequence is altered in mutant alleles of sns. (A) A BamHI site located within an intron of the sns gene is altered in sns^XB3 by a G to A transition in the first G of the BamHI recognition sequence. As confirmed by RT–PCR of mRNA from sns^XB3 mutant embryos, this change introduces a splice acceptor site that results in a spliced product of 248 bp rather than the wild-type product of 195 bp. Direct sequencing of the 248 bp product confirmed the altered sequence indicated in A. (B–D) Non-isotopic RNase cleavage revealed mutations in the putative sns gene in other EMS induced alleles of sns (data not shown). Direct sequencing of these alleles revealed the indicated alterations. (B) sns^ZF1.4 contains a C to T transition that introduces a stop codon at amino acid position 356. (C) sns^XH2 contains a C to T transition that introduces a stop codon at amino acid 465. (D) rost20² a putative mutant allele of the previously described rost gene (Paululat et al. 1995) contains a C to T transition that introduces a stop codon at amino acid position 367 of SNS.