Cloning, chromosomal localization, and characterization of cDNA from a novel gene, SH3BP4, expressed by human corneal fibroblasts.

The cornea contains, as a major element, a transparent stroma produced and maintained by keratocytes (fibroblasts). Through molecular biology studies using cultured human corneal fibroblasts, a cDNA that was shown to be novel was isolated and sequenced. This novel gene product, named SH3-domain binding protein 4 (SH3BP4), contains a 5.6-kb message that is present in normal human corneal fibroblasts and all tissues examined, with higher levels in pancreas, placenta, heart, and kidney. SH3BP4 was localized by FISH analysis to human chromosome 2q37.1-q37.2 near the telomere. The deduced sequence for SH3BP4 was found to contain a 963-amino-acid open reading frame that has homology to a 479-amino-acid protein in GenBank called EH-binding protein. Although the entire sequence of EH-binding protein aligns with SH3BP4, the alignment is not complete or contiguous. Therefore, SH3BP4 has an additional 73 amino acids at the N-terminus and an additional 411 amino acids near the C-terminus that are not present in EH-binding protein. Consensus sequence domains identified in SH3BP4 include a SH3 domain, three N-P-F motifs, a P-X-X-P motif noted for binding to SH3 domains, a bipartite nuclear targeting signal, and a tyrosine phosphorylation site. SH3BP4 homologies and consensus sequence sites indicate that it may be involved in a newly identified cascade of proteins involved in endocytosis, intracellular sorting, and the cell cycle.