A study of the DNA region coding for initiation of precursor rRNA transcription in Lytechinus variegatus.

Abstract

This chapter presents a study on the DNA region coding for initiation of precursor rRNA transcription in Lytechinus Variegates . The ribosomal DNA from the sea urchin L. Variegatus was mapped with various restriction enzymes and with the R-loop technique. Eco RI cuts a tandem rDNA repeat into 4 fragments. The largest Eco RI fragment (5120 bp) encompasses the majority of the nontranscribed spacer (NTS) and overlaps with the precursor rRNA, but does not hybridize with mature 18S rRNA. This NTS region was cloned using Bam HI, and 2 fragments were obtained; the smaller one (1800 bp) hybridized with precursor rRNA. From the size of the precursor molecule, the origin of transcription can be placed about 900 bases from the 5′ end of the 18S sequence. The 1800 bp Bam HI fragment overlaps the 18S rRNA sequence by ca. 300 bp and therefore, extends in the other direction ca. 600 bp beyond the 5′ end of the precursor.