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

Abstract

POLY(A) is a constituent of most animal cytoplasmic mRNAs^1,2 and has been demonstrated in rapidly-labelled, polysomal RNA in plants^3,4. 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 reports^9–11 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).