Abstract
Escherichia coli has a ribonucleoprotein complex that is composed of a 114 nucleotide 4.5S RNA and a 48 kDa polypeptide (P48) that has been demonstrated to function in translation and in the secretion of periplasmic polypeptides. A small RNA of approximately 220 nucleotides has been identified in maize mitochondria that includes sequence identity with the highly conserved domain of the bacterial 4.5S RNA. The transcript is mitochondrially encoded and maps to a region upstream of the gene for ATP synthase subunit I. The mitochondrial 4.5S-like RNA has 15 nucleotides of sequence identity with the highly conserved region of the bacterial 4.5S RNA. Sucrose density gradient centrifugation of a maize mitochondrial lysate demonstrated that the 4.5S RNA is a component of a high molecular weight complex under native conditions, and could be disrupted by phenol. Anti-P48 immune serum immuno-precipitated a mitochondrial protein of approximately 48 kDa, and RNA gel blot analysis of the immunoprecipitation reaction indicated that the 4.5S-like RNA co-immuno-precipitated with the 48 kDa polypeptide. The mitochondrial 4.5S ribonucleoprotein complex could function in translation or protein targeting.
Highlights
The 4.5S RNA is a small bacterial RNA that has been identified from a number of procaryotes [1,2]
In order to determine whether a small mitochondrial transcript with sequence similarity to the procaryotic 4.5S RNA was present in maize mitochondria, RNA gel blots were hybridized with an oligonucleotide probe for the 22 nt conserved domain of 4.5S RNA
The probe detected a transcript of ∼220 nt (Fig. 1), and indicated that a small transcript with sequence similarity to the procaryotic 4.5S RNA was present in maize mitochondria
Summary
The 4.5S RNA is a small bacterial RNA that has been identified from a number of procaryotes [1,2]. The 4.5S gene (ffs) is essential for growth of Escherichia coli [3], and other procaryotic 4.5S genes can complement E.coli strains depleted in the 4.5S RNA [2]. The 4.5S RNA of E.coli is a 114 nucleotide (nt) transcript, and ffs genes from other procaryotes express small structural transcripts of 105–271 nt when expressed in E.coli [2]. The procaryotic 4.5S RNAs have a highly conserved 22 nt domain and conserved secondary structure, the 4.5S RNAs differ in size and have relatively little (29%) sequence identity outside of the conserved domain [2,4]. Suppression analysis of a 4.5S RNA depletion strain of E.coli lead to the identification of suppression mutations that mapped to elongation factor G (EF-G)
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