Mapping of ribosomal RNA transcripts in wheat.

Ribosomal RNA transcripts in wheat have been studied by RNA gel blotting and their termini determined from electrophoretic analysis of S1 nuclease-resistant RNA/DNA hybrids and also of hybrids created by primer extension. A major putative transcription initiation site has been localized 1132 base pairs upstream from the 5' end of the 18S RNA sequence. A major putative processing site occurs 640 base pairs from the 5' end of the 18S RNA. Transcripts extending at least 750 base pairs beyond the 3' end of the 25S rRNA sequence into the array of intergenic repeats are present, as are transcripts covering the principal initiation sequence. This suggests that some transcripts extend through the intergenic DNA from one repeat unit into the next.