CAD (rudimentary)
CAD, also known as a gene called rudimentary, is a nuclear, protein-coding gene that is involved in pyrimidine biosynthesis. (The gene was originally named rudimentary because mutant forms of the gene caused deformed wings in Drosophila.) CAD is a single copy gene and, in Drosophila and Anopheles, it is found on the X chromosome. Full-length CAD sequences are available for Drosophila melanogaster (GenBank accession number AE003503) and Anopheles gambiae (GenBank accession number EAA06526). In Drosophila and other insects, CAD consists of four distinct loci that catalyze the first steps in the de novo pyrimidine biosynthetic pathway: carbamoylphosphate synthetase (CPS), dihydroorotase (DHO), aspartate transcarbamylase (ATC), and glutamate aminotransferase (GAT) (Moulton & Wiegmann 2004, Freund & Jarry 1987). In insects and vertebrates the largest of the CAD domains is the carbamoylphosphate synthase (CPS) domain (Kim et al. 1992). CPS consists of approximately 4 kb of coding sequence, and provided robust support for higher-level, Cretaceous-age divergences in Diptera (Moulton & Wiegmann 2004).
Using the recently published sequence of the honey bee genome, we located the CAD homolog by blasting with fly CAD sequences. We assembled a fragment of CAD that matches very well the large data set assembled for flies by Moulton and Wiegmann (2004). Using this alignment we developed primers for amplifying and sequencing an approximately 3000 bp fragment of CAD in bees (see pdf file below). Based on preliminary tests, these primers work well on a broad survey of ST and LT bees.
Interestingly, CAD contains several small introns (usually 50-60 bp) that vary in presence and absence among taxa. Intron presence/absence could be coded as a character when introns vary in position among taxa (Brady & Danforth 2004). CAD seems to have a slight A/T bias (~60%) in Diptera (Moulton & Wiegmann 2004).
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Gene Information: |
Map of CAD gene (.pdf file) |
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