Expression of spliceosome-associated protein 49 is required for early embryogenesis in Caenorhabditis elegans.

Spliceosome-associated protein 49 (SAP 49) is a subunit of the splicing factor SF3b, which is involved in 3' splice site recognition in pre-mRNA splicing. Here we show the Caenorhabditis elegans SAP 49 gene is located in a gene cluster that is transcribed polycistronically with three other upstream genes. Transgenic analysis of expression of the gene cluster under the control of its native promoter revealed that in spite of its predicted essential function for all cells, the C. elegans SAP 49 expression is limited to specific cells in both larval and adult stages. When the endogenous SAP 49 expression was inhibited by microinjection of an antisense RNA, embryos laid by the injected worms ceased to develop at a specific stage of early embryogenesis, indicating that SAP 49 plays an essential role in the development of C. elegans. These results raise the possibility that SAP 49 is a cell-specific, not constitutive, splicing factor.