The cosmid C11F2 has been shown to rescue two alleles of let-56
, using the technique of germ line transformation (1). Two adjacent PstI subclones of this cosmid detect transcripts on Northern blots. Neither of these two PstI subclones have been shown to rescue let-56
. One PstI subclone (fragment 'q', see 2) detects a 2.4 kb message. This PstI subclone was used to screen a lambda gt10
cDNA library obtained from B. Meyer. This resulted in the isolation of a 1.3 kb cDNA, found to be contained entirely within fragment q. This 1. 3 kb cDNA (called 'C2'; 2) was sequenced and found to contain a single long open reading frame of approximately 1200 nucleotides. This cDNA was incomplete, representing the 3' portion of the expected message (3) . When the inferred amino acid sequence of this single long open reading frame was used to search the translated EMBL DNA databank ( release 20), significant homology was detected with the human growth factor activatable Na+/H+ antiporter protein sequence (3;4). We have commenced sequencing genomic C. elegans Na+/H+ antiporter DNA contained within a 6.2 kb HindIII fragment (called 'FH6'; 2) subcloned from fragment q. This subclone contains all of the C2 cDNA homologous region, plus an additional 800 nucleotides 5' of the C2 homologous sequence. Preliminary results indicate that the 5' end of the C. elegans Na+/H+ antiporter is not entirely contained within the additional 800 nucleotides of genomic DNA immediately upstream of the C2 homologous sequence residing within FH6. Currently, we are attempting to subclone the 5' end of the C. elegans Na+/H+ antiporter gene from fragment q. In addition, we will screen a lambda zap cDNA library obtained from B. Barstead in order to recover a full length Na+/H+ antiporter cDNA. Questions we intend to address include: (1) whether let-56
encodes the C. elegans Na+/H+ antiporter gene and (2) whether the C. elegans Na+/H+ antiporter protein is regulated in a manner similar to its human equivalent.