Upstream sequences confer distinctive transcriptional properties on genes encoding silkgland-specific tRNAAla.

To understand the molecular basis for the tissue-specific accumulation of alanine tRNAs in silkworms, we have compared the transcriptional properties of genes that encode constitutive and silkgland-specific type alanine tRNA. Genes for each class of alanine tRNA behave very differently when used as templates for homologous in vitro transcription. Since these properties are likely related to the activities of the corresponding genes in vivo, we wished to identify the cis-acting elements responsible for them. We have therefore constructed hybrid silkgland-specific/constitutive genes and have analyzed their capacity to direct transcription in vitro. We find a simple pattern: the distinctive transcriptional properties of the two kinds of tRNAAla genes are the result of different positive signals upstream from their sites of transcription initiation.