Department of Biology

Project 1: Analysis, Cloning, Sequencing and Characterization of VNTR like Sequences Present in Chloroplast DNA of C. reinhardti.

Tandem repetitive DNA sequences have been discovered in the genomes of many higher eukaryotes, including humans. These sequences belong to the class of minisatellites of eukaryotic genomes. They tend to be GC-reach and frequently exhibit extensive allelic variation in the number of repeating units. Hypervariable satellites, called VNTR (Variable Number Tandem Repeats) are utilized in forensic DNA analysis using technique called DNA Fingerprinting. The technique takes advantage of the highly polymorphic nature of these repeats in humans. Each repeating unit contains a smaller 16-40 bp core sequence. The number of tandem repeats of core sequence is variable both within a locus and between loci. VNTR sequences have not been associated with any known cellular function, yet their sequences are highly conserved. The study of function of VNTR elements has been hindered by the presence of a large number of them in most of the genomes and the lack of a simple model with a limited number of VNTRs in a small genome. The finding of the presence of a VNTR-like element in the chloroplast genome of Chlamydomonas (Fong and Surzycki, 1993) has provided an excellent model for study of VNTR.

Project 2: The Mechanism of Transposition of Nuclear DNA of Chlamydomonas by the Ds 6.8 Transposon of Corn.

The Ds 6.8 transposon is a non-transposing derivative of the Ac 9 transposon found first in corn by Barbara McClintock. This element cannot transpose due to a deletion of a large portion of the transposase gene. However, this element can be mobilized in the genome in the presence of at least one copy of active transposon by trans complementation. Ds 6.8 element was transformed into the nuclear genome of Chlamydomonas and shown to be able to transpose without the presence of the Ac element (Surzycki and Schwartz). This argues for the presence of an Ac-like transposon in the genome of Chlamydomonas that is normally silenced and immobile. Research is being carried out to clone this Ac-like transposon(s) and determine the mechanisms of its silencing. The silencing of Ac transposon in corn and other plants occurs by transcriptional inactivation of the transposase promoter. This cannot be the case for Chlamydomonas transposon silencing since Ds 6.8 is mobile in these cells. The silencing of the native Chlamydomonas Ac-like transposon represents a novel mechanism of transposon silencing.