Major mRNA species from spinach chloroplasts do not contain poly(A).

Abstract

POLY(A) is a constituent of most animal cytoplasmic mRNAs1,2 and has been demonstrated in rapidly-labelled, polysomal RNA in plants3,4. Verma et al.5 have shown that cellulase mRNA, isolated from auxin-treated pea epicotyls, contains poly(A). Although a significant proportion of eukaryotic polysomal mRNAs are known to lack poly(A)6–8, the presence of poly(A) is still regarded as a characteristic feature of unfractionated preparations of eukaryotic mRNA. By contrast, poly(A) has not been detected in mRNA from prokaryotic cells8. Several reports9–11 have indicated that poly(A) is present in HeLa cell mitochondrial RNA, although Groot et al.12 were unable to detect poly(A) in yeast mitochondrial RNA. Here we describe experiments in which we have assayed for the presence of poly(A) in spinach chloroplast RNA by two methods; (1) hybridisation of chloroplast RNA with 3H-poly(U) and (2) binding of chloroplast RNA, pulse-labelled in vivo, to oligo(dT) cellulose. Additionally, the mRNA activities of chloroplast poly(A)-containing RNA and non-poly(A)-containing RNA (hereafter referred to as poly(A)+ RNA and poly(A)− RNA respectively) have been investigated by measuring their translation into specific polypeptides in cell-free extracts from Escherichia coli. From the results, we conclude that chloroplast mRNA lacks poly (A).