Translation of satellite tobacco necrosis virus ribonucleic acid. II. Initiation of in vitro translation in procaryotic and eucaryotic systems

Identification and characterization of a biosynthetic precursor (preprolactin) of ovine pituitary prolactin

Poly(A)-containing mRNA prepared from ovine anterior pituitary glands stimulated the incorporation of radioactivity into protein in a wheat germ cell-free system from 7- to 25-fold over background. Approximately 30% of the total protein synthesized could be precipitated by antiserum to prolactin, indicating that a molecule which shares antigenic determinants with prolactin was being synthesized. Analysis of the immunoprecipitable cell-free translation product, by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulphate demonstrated the presence of a prolactin-like molecule with a molecular weight greater than that of prolactin itself. Partial N-terminal sequence analysis of the immunoprecipitable translation product showed that it contained one methionine residue at position 1 and several leucine residues within the first 30 amino acids. Experiments with labelled initiator and internal met tRNAMet indicated that the product being synthesized contained the initiating methionine and was probably the initial translation product of prolactin mRNA.

Effect of capping upon the mRNA properties of satellite tobacco necrosis virus ribonucleic acid

The mRNA guanyltransferase-mRNA methyltransferases of vaccinia virions can be used to introduce a 5'-terminal m7g(5')pp(5')Apm... capping group onto the RNA of satellite tobacco necrosis virus (STNV RNA) to yield intact capped STNV RNA. Studies with an in vitro system from wheat germ and limiting quantities of capped and uncapped STNV RNA show that the rates and extents of formation of initiation complexes of protein synthesis by intact capped and uncapped STNV RNA are identical, suggesting that 5'-terminal cap groups cannot function in the translation of STNV RNA. Also, the cap analogue pm7G equally inhibits the initiation and the translation of limiting quantities of both capped and uncapped STNV RNA. These contrasting observations suggest that the wheat germ system contains a pm7G sensitive protein and that STNV RNA has a tertiary structure that restricts the function of an added 5'-terminal capping group. This theory is supported by observations that fragmented capped STNV RNA is better at forming initiation complexes than is equally fragmented uncapped STNV RNA.

Nucleotide sequence of the 5' terminus of satellite tobacco necrosis virus ribonucleic acid

Treatment of the RNA of satellite tobacco necrosis virus (STNV) with phosphomonoesterase followed by heat denaturation and treatment with polynucleotide kinase in the presence of [gamma-32P]ATP yields a STNV [5'-32P]RNA containing a homogeneous 5' terminus. Analyses of this STNV [5'-32P]RNA yield the sequence of the first 42 nucleotides from the 5'terminus of STNV RNA. This nucleotide sequence contains the translation initiation AUG codon starting at position 30 from the 5' terminus as indicated by match of subsequent nucleotides with the genetic code assignments for the N-terminal amino acids of STNV coat protein in the 5'-terminal sequence ppAGUAAAGACAGGAAACUU-UACUGACUAACAUGGCAAAACAAC. An interesting feature of this sequence is its potential to form a hairpin loop structure involving perfect Watson-Crick base pairing between the first seven nucleotides and nucleotides at positions 16--22.

Partial amino acid sequence of rat pre-prolactin

Rat pituitary mRNA was used to direct the cell-free synthesis of pre-prolactin labelled with [4,5-3H]leucine and either [35S] methioninc or [35S] cystine. Sequence analysis of the labelled protein indicates that pre-prolactin has 29 amino acid residues joined to the N-terminus of the prolactin sequence. Leucine residues were found at positions 13, 14, 15, 16, 21 and 22, methionine residues at positions 1, 17 and 18, and a cysteine residue at position 24 of the precursor sequence, and this partial sequence shows considerable similarity with other precursors that have been sequenced.

Translation of satellite tobacco necrosis virus ribonucleic acid by an in vitro system from wheat germ

The RNA of satellite tobacco necrosis virus (STNV) is an effective messenger RNA when translated in an in vitro system from wheat germ. This RNA codes for only STNV coat protein, as indicated (1) by coincidence of the tryptic fingerprints of the translation product and of STNV coat protein, (2) by equivalent size of the translation product and STNV coat protein, and (3) by isolation of an initial peptide of the in vitro product containing the amino acid sequence of the N terminus of STNV coat protein. STNV RNA does not contain a 5'-terminal m7G(5')ppp(5')Np---group and translation of STNV RNA by the wheat germ system does not involve prior formation of 5'-terminal m7G(5')ppp(5') nP---groups on STNV RNA. STNV RNA and 125I-labeled STNV RNA form a specific initiation complex when incubated with initiator tRNA, GTP, initiation factors, and wheat germ ribosomes. Treatment of this specific initiation complex with ribonuclease A allows isolation of an 125I-labeled oligonucleotide protected from ribonuclease A by the initiation complex. This specific oligonucleotide contains approximately 38 nucleotides, including nucleotide sequences that coincide with the codons of the N-terminal amino acids of STNV coat proteins.

Cell-free synthesis of rat preproinsulins: characterization and partial amino acid sequence determination

Whole nucleic acid fractions of isolated rat islets of Langerhans greatly stimulate incorporation of radioactive amino acids into protein in a wheat germ ribosomal system. Approximately 30% of the synthetic product is precipitated with antisera to insulin or proinsulin. Characterization of this material by gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates a molecular mass of 11,500 daltons. Trypsin digestion releases intact A chain as well as tryptic fragments of the C-peptides and B chains of the two rat proinsulins. Automated sequence determination of labeled cell-free product purified by immunoprecipitation discloses the presence of 23 additional amino acids NH2-terminal to the B chain sequence of proinsulin. The partial amino acid sequence of this extension is as follows: NH2-X-Leu (Lys) Met-x-Phe-Leu-Phe-Leu-Leu (Lys) Leu-Leu-x-leu-X-X-X-X-X-X-X-X-proinsulin. On the basis of the above evidence we have designated this peptide preproinsulin.

NH2-terminal amino acid distribution and amino acid composition of Streptococcus faecalis R soluble and ribosomal proteins

The NH(2)-terminal amino acid distribution of Streptococcus faecalis R soluble and ribosomal proteins isolated from cells at different stages of growth on either folate-sufficient or folate-deficient medium was determined by the dinitrophenyl method. The NH(2)-terminal residues do not follow the random distribution observed for the total amino acid composition of S. faecalis soluble and ribosomal proteins. Methionine and alanine occur most frequently; serine, threonine, aspartic and glutamic acids, and glycine are also present at the NH(2)-terminal position of S. faecalis R proteins. The absence of folic acid yields cells that are incapable of formylating methionyl-transfer ribonucelic acid tRNA(f) (Met), but does not affect either the qualitative or quantitative NH(2)-terminal distribution of total soluble or total ribosomal proteins compared to cells grown with folate. A small quantitative difference was observed in the frequency of distribution of certain amino acids at the NH(2)-termini between log and stationary phase soluble proteins. The amino acid residues found at the NH(2)-terminal position of S. faecalis proteins are qualitatively similar to those reported for several other organisms.