Human and mouse LSP1 genes code for highly conserved phosphoproteins.

With use of the mouse LSP1 cDNA we isolated a human homologue of the mouse LSP1 gene from a human CTL cDNA library. The predicted protein sequence of human LSP1 is compared with the predicted mouse LSP1 protein sequence and regions of homology are identified in order to predict structural features of the LSP1 protein that might be important for its function. Both the human and mouse LSP1 proteins consist of two domains, an N-terminal acidic domain and a C-terminal basic domain. The C-terminal domains of the mouse and human LSP1 proteins are highly conserved and include several conserved, putative serine/threonine phosphorylation sites. Immunoprecipitation of LSP1 protein from 32P-orthophosphate-loaded cells show that both the mouse and human LSP1 proteins are phosphoproteins. The sequences of the putative Ca2(+)-binding sites present in the N-terminal domain of the mouse LSP1 protein are not conserved in the human LSP1 protein; however, a different Ca2(+)-binding site may exist in the human protein, indicating a functional conservation rather than a strict sequence conservation of the two proteins. The expression of the human LSP1 gene follows the same pattern as the expression of the mouse LSP1 gene. Southern analysis of human genomic DNA shows multiple LSP1-related fragments of varying intensity in contrast to the simple pattern found after similar analysis of mouse genomic DNA. By using different parts of the human LSP1 cDNA as a probe, we show that most of these multiple bands contain sequences homologous to the conserved C-terminal region of the LSP1 cDNA. This suggests that there are several LSP1-related genes present in the human genome.