Structure of the human lck gene: differences in genomic organisation within src-related genes affect only N-terminal exons.

Although cDNA sequences coding for several Rous sarcoma virus Src-related protein tyrosine kinases (PTKs) have been reported for several years, knowledge of the structure and organisation of genes of the src family is still limited. In this work, a detailed structure and organisation of the human lck gene is reported. A 17-kb genomic clone encoding human p56 Lck, a lymphocyte-specific PTK of the Src-related subfamily, has been isolated. The human lck gene is organized in 13 exons, one more than in the human cellular (c)-src gene. The twelve coding exons are located in this clone, whereas the putative 5'-noncoding exon is probably located very far upstream from the second exon. Splicing sites for exons 4 to 12, which encode both conserved phospholipase-C-like and catalytic domains of the Src-like PTKs, arise exactly at the same position for the human lck, human c-src and c-fgr genes. The only differences concern the splice sites of exons 1' and 2, which encode the unique N-terminal domain of human Lck. These results give further evidence that the different PTKs of the Src-like family have probably evolved through the mechanism of exon shuffling.

Comparative value of polymerase chain reaction and conventional biological tests for the prenatal diagnosis of congenital toxoplasmosis.

When toxoplasmosis is acquired during pregnancy, there is a risk of severe congenital defect in the foetus. Maternal treatment with spiramycin limits the transplacental passage of the parasite to the foetus but does not prevent infection in all cases. Prenatal diagnosis should be based on specific and fast methods to prescribe the more potent combination of sulfadiazine and pyrimethamine. This study evaluates PCR in the prenatal diagnosis of toxoplasmosis; PCR was based on the detection of the gene coding for the P30 surface protein. Amniotic fluid from 44 women with suspected foetal infection was tested by PCR and results were compared to those of conventional diagnostic tests on foetal blood and amniotic fluid. PCR was positive in 7 out of 10 samples from proven congenital toxoplasmosis cases. Sensitivity of PCR was similar to cell culture and mouse inoculation of amniotic fluid but was superior to tests carried out on foetal blood (specific IgM, eosinophil and platelet counts, gamma glutamyl transferase, mouse inoculation). In two cases, PCR was positive with no detected infection of the foetus. In this study, the combination of fast detection methods, ie cell culture and PCR of amniotic fluid, eosinophil and platelet counts, GGT activity and specific IgM, enabled us to confirm 10/10 cases of congenital toxoplasmosis in less than a week. PCR therefore appears to be an additional test which improves early prenatal diagnosis of toxoplasmosis.

DNA restriction polymorphism of alpha-fetoprotein gene after digestion by MspI endonuclease.

Hybridization of alpha-fetoprotein clones cDNA with human DNAs digested by seven restriction endonucleases reveals one polymorphism. This polymorphism, detected after restriction by MspI, is at low frequency (f = 0.02) and is validated by family analysis. It corresponds to an intronic sequence, for a methylated site external to the probes utilized.