5'-flanking sequences required for efficient transcription in vitro of 5S RNA genes, in the related nematodes Caenorhabditis elegans and Caenorhabditis briggsae.

In the nematode C. elegans, we had previously observed apparent species specificity in 5S RNA transcription. We have now undertaken a further study of 5S RNA gene transcription in this organism and in the related nematode, C. briggsae; the latter was chosen because it might show evolutionarily conserved, functionally important features. Deletion mutagenesis and transcription in vitro, followed by more precise replacements of short blocks of 5' sequence, show that a short, TATA-like sequence at -25 is essential for efficient transcription in vitro of the 1.0-kb C. elegans 5S DNA repeat, and of both C. briggsae 0.7- and 1.0-kb 5S DNA repeats. Internal sequences within the 5S RNA gene appear to be required and can compete for limiting transcription components, whereas 5' flanking sequences do not. These observations suggest that the process of 5S RNA transcription is similar in these nematodes and other higher eukaryotes.