Spiroplasma citri UGG and UGA tryptophan codons: sequence of the two tryptophanyl-tRNAs and organization of the corresponding genes.

AUTOR(ES)

Citti, C

RESUMO

From the total tRNAs of Spiroplasma citri, we isolated and purified two tRNA(Trp) species by using chromatography on an RPC-5 column followed by denaturing polyacrylamide gel electrophoresis. The sequence of the two tRNAs, as well as the sequences of the corresponding genes, were determined. One of the two tRNA(Trp) species has a CCA anticodon and is able to pair with the universal UGG tryptophan codon, while the second has a U*CA (U* is a modified uridine) anticodon and is able to pair with UGA but also with UGG in accordance with the "U:N wobble" rule. Thus, in S. citri, UGA is not a stop codon but codes for tryptophan. The two tRNA(Trp) genes, together with a third tRNA gene, tRNA(Ser) (CGA), belong to a single transcription unit. The nucleotide sequences of the two tRNA(Trp) species show 82.9% similarity. The two spiroplasmal tRNA(Trp) species can be aminoacylated by using an aminoacyl-tRNA synthetase fraction from S. citri. In contrast, the enzyme fraction from Escherichia coli aminoacylates tRNA(Trp) (CCA) but not tRNA(Trp) (U*CA).

Documentos Relacionados

• Nucleotide sequence containing the maize chloroplast proline (UGG) and tryptophan (CCA) tRNA genes.
• Yeast tRNATrp genes with anticodons corresponding to UAA and UGA nonsense codons.
• Spiralins of Spiroplasma citri and Spiroplasma melliferum: amino acid sequences and putative organization in the cell membrane.
• Nucleotide sequence of the Spiroplasma citri fibril protein gene.
• Integrative and free Spiroplasma citri oriC plasmids: expression of the Spiroplasma phoeniceum spiralin in Spiroplasma citri.