University of California, Irvine, Department of Biological Sciences, Molecular Biology and Biochemistry

Dr. Krishna K. Tewari

(Ph.D., Lucknow University (India), 1960)

Chloroplast DNA; replication and transcription

  • Faculty Profile

    Publications via PubMed (NIH National Library of Medicine)

  • E-mail: kktewari@uci.edu

    • Our laboratory is investigating the structural organization of genes in chloroplast DNA (ctDNA), replication of ctDNA, and transcription of ctDNA genes. Chloroplast DNAs of higher plants exist as homogenous double-stranded, closed-circular DNA molecules of 120 kbp to 160 kbp. The ctDNA codes for its own ribosomal RNA, tRNAs and about 60-80 proteins.

    Replication of ctDNA proceeds from two origins located within separate displacement loops (D-loops). The two D-loops have been mapped by electron microscopic analysis on restriction digests of supercoiled ctDNA. One D-loop (Ori A) resides in the spacer region between the 16S and 23S rRNA genes while the other (Ori B) is located at the 3'-end of the 23S rRNA gene. Ori A contains some stem-loop structures as well as some repeated sequences. An in vitro replication system has been developed from chloroplasts that faithfully replicates Ori A containing recombinant plasmids. In addition, these recombinants are capable of transforming plant tissue culture cells when delivered by high velocity particles. The DNA polymerase as well as topoisomerase I and a DNA primase have been purified in our laboratory. The fine structure mapping of Ori A and the purification of other replication proteins are currently underway.

    The other project in our laboratory is focused on transcription of the ctDNA genes. A transcriptional complex from chloroplasts has been purified that contains twelve polypeptides. Monoclonal antibodies to these proteins have been obtained and their functional roles are being studied by photo-crosslinking. A template binding protein of apparent 150 KDa has been identified which interacts with both chloroplast ribosomal and messenger RNA promoters. Photo-crosslinking has also identified a 48 kDa polypeptide which is associated with nascent transcripts during transcription. Other polypeptides are being studied by similiar techniques and the genes for these proteins are being characterized.

    Selected Publications
    Khanna, N.C., S. Lakhani and K.K. Tewari. 1991. Photoaffinity labelling of the pea chloroplast transcriptional complex by nascent RNA in vitro. Nucleic Acids Res. 19:4849.

    Nielsen, B., V.K. Rajashekhar and K.K. Tewari. 1991. Pea chlorplast DNA primase: characterization and role in initiation of replication. Plant Mol. Biol. 16:1019.

    Rajashekhar, V.K., E. Sun, R. Meeker, B.-W. Wu and K. Tewari. 1991. Highly purified pea chloroplast RNA polymerase transcribes both tRNA and mRNA genes. Eur. J. Biochem. 195:215.

    Dr. Tewari is part of the UCI Graduate Track in Structural Biology and Molecular Biophysics within the UCI graduate Program in Molecular Biology, Genetics, and Biochemistry. Applications requests or additional information about the graduate program may be obtained by electronic mail at gp-mbgb@uci.edu or by phone at (949) 824-8145. On-line applications may also be submitted through the Office of Research and Graduate Studies.

    1) Molecular Biology, Genetics, and Biochemistry

    2) Email: gp-mbgb@uci.edu or call (949) 824-8145

    3) Graduate Studies Home Page, with links to On-line applications and the Office of Research and Graduate Studies

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