Ribosomal protein L5 of Bombyx mori: cDNA sequence and tissue differences in the L5 mRNA content

A gene encoding the ribosomal protein L5, which assembles with the 5S rRNA into one of the components of the 60S ribosomal subunit, was identified in insects for the first time. We report on the isolation of Bombyx mori cDNA, whose putative translation product is 60-76% identical with the L5 sequences known from other animals and about 50% identical with the L5 of rice and yeasts. Bombyx contains a single copy of the L5 gene, which is constitutively expressed as a 1.1 kb mRNA in all tissues. The ratio of L5 mRNA to total RNA appears to reflect the proteosynthetic tissue capacity. A very high level of L5mRNA is maintained in functional silk glands. A rapid decline of the ratio of L5mRNA to the rRNA, which occurs in the silk glands after cocoon spinning, indicates differences in the stability of these two RNA classes.