Structural organization of the transfer RNA operon I of Vibrio cholerae: differences between classical and El Tor strains.

Nine major transfer RNA (tRNA) gene clusters were analysed in various Vibrio cholerae strains. Of these, only the tRNA operon I was found to differ significantly in V. cholerae classical (sixth pandemic) and El Tor (seventh pandemic) strains. Amongst the sixteen tRNA genes contained in this operon, genes for tRNA Gln3 (CAA) and tRNA Leu6 (CUA) were absent in classical strains as compared to El Tor strains. The observation strongly supported the view that the above two pandemic strains constitute two different clones.

Partial sequence of the rRNA operon of Pneumocystis carinii isolates from Puerto Rico

Several reports indicate geographic variation of isolates of Pneumocystis carinii hominis. We have sequenced the internal transcribed spacer (ITS) region and large subunit Group I intron of rRNA genes from P. carinii DNA obtained from two patients from Puerto Rico. Both can be subclassified as Type II, according to the sequence of the ITS region. A system capable of identifying individual isolates will be an essential tool for epidemiological studies of the organism. The amplification of DNA from fixed tissues may facilitate the processing of a large number of samples.