Molecular analysis of odd-skipped, a zinc finger encoding segmentation gene with a novel pair-rule expression pattern.

odd-skipped (odd) is one of eight known pair-rule genes that establish portions of alternating segments during Drosophila embryogenesis; odd mutant embryos exhibit pattern defects in anterior regions of odd-numbered segments. P element transposon tagging was used to clone 25 kb of DNA from the odd genomic region. Molecular analysis of phenotypic revertants confirmed that the P element used to tag the locus was responsible for the corresponding odd mutation, and significant structural changes were identified in two additional odd mutants. Several cDNA clones derived from a 2.2 kb embryonic transcript were isolated and the longest was sequenced. The predicted odd protein of 392 amino acids is highly basic and contains four tandem Cys-Cys/His-His zinc finger repeats, consistent with a presumed function for odd as a DNA binding protein and transcriptional regulator. In situ hybridization analysis indicated that odd transcripts accumulate in a dynamic pattern during early embryogenesis, with two temporally distinct modes of expression. The first mode results in a 'pair-rule' pattern of seven stripes at the blastoderm stage, representing the expected double segment periodicity. During gastrulation, the seven primary stripes are supplemented by secondary stripes which appear in alternate segments, resulting in the equivalent labeling of every segment in the extended germ band. Similar double to single segment transitions have now been reported for four of the six pair-rule genes analyzed.