CLONING AND EVALUATION OF RALGDS AS A CANDIDATE FOR THE TUBEROUS SCLEROSIS GENE TSC1

RALGDS is a 115 kDa protein which was identified by its ability to enh ance guanine nucleotide exchange for the ras family member ral. It als o binds to activated ras and rap1, and appears to function as part of a signalling complex in downstream events following rap1 activation. H ere we report the identification of full-length cDNA clones for human RALGDS, isolated front a brain cDNA library. The predicted protein has strong sequence homology to rat and murine isoforms of RALGDS in the N- and C-terminal regions, but an internal region (aa 250-380) shows r elatively high divergence with only 42% identical amino acid residues. The human RALGDS gene is contained within a 30 kb region of 9q34, app roximately 200 kb proximal to the ABO gene, within the current critica l region for the tuberous sclerosis gene TSC1. Partial genomic structu re was determined; it consists of at least 11 exons. Based upon analys is of Southern blots from 110 TSC patients, genomic DNA SSCP analysis, and RT-PCR analysis which demonstrated RNA expression of both alleles in patients from 9q34-linked TSC families using intragenic polymorphi sms, we conclude that RALGDS is not likely to be TSC1.