Cloning of developmentally regulated genes from Leishmania major and expression following heat induction

The protozoa Leishmania undergo morphological and biochemical transformation from the promastigote to the amastigote form during their life cycle. To characterize this transformation process, we constructed a cDNA library for the promastigote stage of Leishmania major and used differential cDNA hybridization to identify cDNA sequences expressed at different abundance in promastigotes or amastigotes of L. major. P100/11E is a single copy gene whose 1600-nucleotide mRNA is enriched in promastigotes. P101/10 is a repeated gene whose 3300-nucleotide transcript is enriched in amastigotes. These developmentally regulated genes are not linked in the genome of L. major and are located on separate chromosome bands. The abundance of the P101/10 transcript increases severalfold during the transformation process at 37 degrees C in vitro and is thermally induced within 3 h after transfer of promastigotes from 27 to 37 degrees C. Examination of beta-tubulin gene expression showed that the relative abundance of the 3400-nucleotide beta-tubulin RNA is decreased at 37 degrees C in vitro. Our results indicate that the expression of two developmentally regulated genes of L. major is controlled at the level of mRNA abundance and provide direct evidence that thermal induction plays a general role in regulating gene expression in Leishmania.

Peculiar sequence organization of kinetoplast DNA minicircles from Trypanosoma cruzi

The sequences of two minicircles from the kinetoplast DNA of the CL strain and one of the Y strain of Trypanosoma cruzi are reported. These 1.4 kb molecules have a peculiar sequence organization, the most distinctive feature being the occurrence of a 120 bp sequence repeated four times, located at 0, 90, 180 and 270 degrees along each circle. We have termed these conserved regions in this species 'minirepeats'. Minirepeats have a 3-fold higher concentration of cytosine residues in comparison with the variable regions and contain the universal 12-mer motif GGGGTTGGTGTA present in all sequenced minicircles and which was shown to be involved in DNA replication. A consensus sequence of T. cruzi minirepeats was determined using the 20 minirepeats present in five known T. cruzi minicircle sequences. This consensus sequence contains regions which have been remarkably well preserved in strains which show great biological diversity. In addition a low level of intraminicircle sequence similarity was also observed within the variable region, but this similarity did not extend between strains. The abundance of conserved minirepeat sequences containing invariant restriction sites in T. cruzi cells may prove valuable for the development of new direct diagnostic methods for Chagas' disease based on DNA probe technology.

Sequence heterogeneity and anomalous electrophoretic mobility of kinetoplast minicircle DNA from Leishmania tarentolae

Several unit-length minicircles from the kinetoplast DNA of Leishmania tarentolae were cloned into pBR322 and into M13 phage vectors. The complete nucleotide sequences of three different partially homologous minicircles were obtained. The molecules contained a region of approx. 80% sequence homology extending for 160-270 bp and a region unique to each minicircle . A 14-mer was found to be conserved in all kinetoplast minicircle sequences reported to date. The frequency distributions of various minicircle sequence classes in L. tarentolae were obtained by quantitative gel electrophoresis and by examination of the "T ladder" patterns of minicircles randomly cloned into M13 at several sites. By these methods we could assign approx. 50% of the total minicircle DNA into a minimum of five sequence classes. A sequence-dependent polyacrylamide gel migration abnormality was observed with several minicircle fragments both cloned and uncloned. The abnormality was dependent on the presence of a portion of the conserved region of the minicircle .