The major goals of this project are to determine the molecular mechanisms of heteroduplex DNA base mismatch correction in Streptococcus pneumoniae and to assess the presence of related systems of generalized mismatch repair in other organisms. In S. pneumonia such repair occurs after DNA-mediated chromosomal transformation and after potentially mutagenic base substitution in DNA replication. Chromosomal mutations called hex block action of the repair system. Two unlinked genes, hexA and hexB, encode proteins implicated in the repair process. The genes have been cloned and their sequences determined. In addition to recognizing a mismatch, which can be an abnormal base pair or a short insertion/deletion, the system targets the strand to be corrected on the basis, apparently, of single-strand breaks bracketing the mismatch. These breaks can be a distance of kilobase or more from the mismatch.
One aim i s to ascertain whether the breaks in nascent DNA giving Okazaki fragments are responsible for targeting, and how these breaks, which appear to be present in the leading as well as the lagging strand being synthesized, are made. The possible role of the DNA glycosylases and AP-endonucleases in causing breaks in the leading strand will be investigated. During repair, a target strand segment containing the mismatch is apparently destroyed. The role of a pneumococcal DNA polymerase, which has been cloned, in restoring the DNA strand within the resulting gap will be tested. The HexA protein will be purified, with the help of an antibody directed to it, and the protein will be characterized with respect to its binding to ATP and to DNA mismatches. HexB will also be purified. A possible requirement for ATP hydrolysis by a complex of HexA and HexB scanning the DNA target for strand breaks and mismatches will be investigated. The anti-HexA antibody will be used to detect cross-reacting proteins in human cell extracts. Preliminary results indicate such a cross-reacting protein. This protein will be isolated and compared to HexA and to a possibly homologous protein encoded by a gene adjacent to dhfr. A human protein homologous to HexB will be similarly sought, and cDNAs encoding both homologs will be obtained. They will be used to assess the role of mismatch repair in preventing the accumulation of mutations that cause ageing and to test whether a genetic defect in the system results in the progeric disease of Werner's Syndrome.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI014885-18
Application #
2060121
Study Section
Microbial Physiology and Genetics Subcommittee 2 (MBC)
Project Start
1978-04-01
Project End
1997-03-31
Budget Start
1995-04-01
Budget End
1996-03-31
Support Year
18
Fiscal Year
1995
Total Cost
Indirect Cost
Name
Associated University-Brookhaven National Lab
Department
Type
DUNS #
City
Upton
State
NY
Country
United States
Zip Code
11973
Lacks, S A; Ayalew, S; de la Campa, A G et al. (2000) Regulation of competence for genetic transformation in Streptococcus pneumoniae: expression of dpnA, a late competence gene encoding a DNA methyltransferase of the DpnII restriction system. Mol Microbiol 35:1089-98
Zhang, Y B; Ayalew, S; Lacks, S A (1997) The rnhB gene encoding RNase HII of Streptococcus pneumoniae and evidence of conserved motifs in eucaryotic genes. J Bacteriol 179:3828-36
Lacks, S A (1997) Cloning and expression of pneumococcal genes in Streptococcus pneumoniae. Microb Drug Resist 3:327-37
Kumaresan, K R; Springhorn, S S; Lacks, S A (1995) Lethal and mutagenic actions of N-methyl-N'-nitro-N-nitrosoguanidine potentiated by oxidized glutathione, a seemingly harmless substance in the cellular environment. J Bacteriol 177:3641-6
Lacks, S A; Greenberg, B; Lopez, P (1995) A cluster of four genes encoding enzymes for five steps in the folate biosynthetic pathway of Streptococcus pneumoniae. J Bacteriol 177:66-74
Diaz, A; Lacks, S A; Lopez, P (1994) Multiple roles for DNA polymerase I in establishment and replication of the promiscuous plasmid pLS1. Mol Microbiol 14:773-83
Lopez, P; Lacks, S A (1993) A bifunctional protein in the folate biosynthetic pathway of Streptococcus pneumoniae with dihydroneopterin aldolase and hydroxymethyldihydropterin pyrophosphokinase activities. J Bacteriol 175:2214-20
Diaz, A; Pons, M E; Lacks, S A et al. (1992) Streptococcus pneumoniae DNA polymerase I lacks 3'-to-5' exonuclease activity: localization of the 5'-to-3' exonucleolytic domain. J Bacteriol 174:2014-24
Diaz, A; Lacks, S A; Lopez, P (1992) The 5' to 3' exonuclease activity of DNA polymerase I is essential for Streptococcus pneumoniae. Mol Microbiol 6:3009-19
Chen, J D; Lacks, S A (1991) Role of uracil-DNA glycosylase in mutation avoidance by Streptococcus pneumoniae. J Bacteriol 173:283-90

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