Mode of inheritance and evidence for cistron heterogeneity of chloroplast 16S ribosomal RNA genes in Nicotiana

Abstract

Oligonucleotide maps (fingerprints) of T1 RNase digests of 125I-labeled 16 S chloroplast rRNA of Nicotiana tabacum and N. gossei revealed the presence of T1 oligonucleotide fragment 100 in the 16 S rRNA of N. gossei while N. tabacum 16 S rRNA had a unique T1 oligonucleotide (fragment 101) as well as some fragment 100. From the positions in the fingerprints and from fingerprints of secondary enzymatic digestion of the fragments, we conclude that fragments 100 and 101 are similar in sequence and size, but fragment 100 probably contains an extra uracil residue. This difference is shown to be maternally inherited, thus confirming the location of 16 S chloroplast rRNA genes on chloroplast DNA and ruling out the possibility of genetically active chloroplast rRNA genes in the nucleus. The presence of both fragments 100 and 101 in N. tabacum may indicate sequence heterogeneity between the two cistrons for 16 S chloroplast rRNA. These results demonstrate the feasibility of determining the inheritance of organelle genes by genetic analysis of their primary transcripts.