ABSTRACT
Eukaryotic transfer ribonucleic acid (tRNA) genes and 5S ribosomal ribonucleic acid genes, transcribed by eukaryotic ribonucleic acid (RNA) polymerase III are well known to have split intragenic promoter sequences, called the 5'- and 3'-intemal control regions. Specific tRNA isoacceptors for glycine, serine, and alanine, whose codon usage is commensurate with the predominant amino acids in the secretory proteins fibroin and sericin, undergo dramatic adaptive changes in tRNA gene expression in the posterior silkgland of Bombyx mori. The primary differences between the two silkworm alanine tRNA transcription units are in the 5'-flanking sequences, such that the sequences of the upstream regions differ in three corresponding places. The results of Gross and co-workers strongly suggest that tRNA genes, tRNA allogenes, and even tRNA pseudogenes are differentially expressed in vivo, and again, that the flanking regions are probably implicated in the observed transcriptional differences between the members of a eu.
