Isolation and characterization of four mouse ribosomal-protein-L18 genes that appear to be processed pseudogenes.

We describe the isolation and initial characterization of six independent lambda Charon 4A recombinant phages which carry four mouse genes for ribosomal protein L18 (L18-15, L18-17, L18-18, L18-30). Structural analysis indicates that these L18 genes contain the entire coding sequence (approx. 600 bp), but lack introns and differ both in their flanking and coding sequences. Based on these features we propose that these are processed pseudogenes. However, we have no indications whether these genes are expressed at either the transcriptional or translational levels. Quantitative estimation of sequence divergence of these genes suggest that the order of their evolutionary emergence (integration) is: first L18-17 and L18-18, then L18-15 and finally L18-30. We discuss the implication of the high proportion of L18 processed genes in this multigene family with respect to the coordinate regulation of r-proteins.