Genes differing in steady-state RNA levels between wild-type N2 and
daf-2 adults and N2 dauer larvae have been previously identified using Serial Analysis of Gene Expression (SAGE). By screening the candidate longevity genes with RNAi, we identified
zip-5 (encoding a basic leucine zipper transcription factor) for further study. A
zip-5 knockout strain has extended longevity (~40% increase in mean life span) compared to N2. A double mutant with
daf-2(
e1370) was shown to have no significant increase in longevity relative to
daf-2 alone, suggesting that the
zip-5 phenotype is
daf-2 dependent. 1 kb of genomic sequence 5 of the confirmed
zip-5 SL1 splice site contains a possible DAF-16 binding site as well as three GATA motifs. By using a series of truncated promoters to drive GFP expression, in vivo activity for these DAF-16 binding sites was observed. One DBE (DAF-16 Binding Element) consensus site, found only once at -492 bp, appears to repress transcription. This is in agreement with the SAGE data showing down-regulation of this transcription factor in an activated DAF-16 background. In addition, exposure of a strain expressing a ZIP-5::GFP fusion protein to
daf-16 RNAi shows increased expression over the control. By contrast, the GATA motifs are required for transcription. RNAi for the GATA transcription factor
elt-2 reduced reporter gene expression. ZIP-5 appears to antagonize long life and its inhibition by DAF-16 may be responsible for a portion of the
daf-2 longevity phenotype.