Fig. 1. The Drosophila genome contains six Skp1-related genes. (A) Partial phylogenetic tree of eukaryotic Skp1 homologs. ORFs homologous to human Skp1 and the related ElonginC gene were identified from the genomes of Saccharomyces cerevisiae (Sc), Schizosaccharomyces pombe (Sp), Caenorhabditis elegans (Ce), Arabidopsis thaliana (At), Drosophila melanogaster (Dm), and humans (Hs), and the predicted protein sequences were aligned using ClustalW and displayed as a phenogram. The six Drosophila Skp1-related proteins share 43-76% identity with human Skp1. Only one human Skp1 gene is known to be complete and expressed. Clusters of Skp1-related genes restricted to a single species have been grouped for clarity. (B) Expression of Drosophila skp genes during development. Northern blots of mRNA from different developmental stages (0-2- and 2-20-hour-old embryos, 3rd instar larvae, adult females, and adult males, respectively) were probed for skpA, skpB or a mixture of skpC and skpD (combined because the two transcripts could not be reliably distinguished by hybridization). Signal from the skpB probe in embryos may result from cross-hybridization with the abundant skpA transcripts. Two images of each blot are shown, with the signal scaling increased 100-fold in the bottom images to compensate for the differences in signal levels. Relative amounts of mRNA in each lane were determined by quantifying the signal obtained using an rp49 probe. (C) Representation of Drosophila skp genes in EST databases. cDNAs corresponding to five of the six Drosophila skp genes were identified, indicating that they are bona fide genes, although skpA ESTs were 10- to 80-fold more common than the other skp genes.

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