Ph.D. - University of California, Berkeley, 1984
Associate Professor
Dept. of Chemistry & Biochemistry
University of Maryland
College Park, MD 20742
Phone: (301)-405-1821
E-mail: dj13@umail.umd.edu
Professor Julin's research interest is in the mechanism, structure, and function of enzymes whose substrate is DNA. The macromolecular nature of nucleic acids leads to unique properties of the enzymes which act on them, including catalysis of topological or structural changes; processive action, in which multiple catalytic events occur during a single interaction of enzyme and substrate; and recognition of specific nucleotide sequences vs. non-specific binding.
Work to date has centered on the recBCD enzyme from Escherichia coli, an enzyme which acts in genetic recombination in the cell. It is a complex multifunctional enzyme consisting of three subunits and has ATP-dependent nuclease activity, DNA-dependent ATPase activity, and DNA helicase (unwinding) activity. The understanding of the interaction of three enzyme subunits with each other and with the ATP and DNA substrates to catalyze these reactions is sought.
It has been shown previously that the recB and recD subunits of the enzyme have binding sites for ATP. The investigation of the catalytic role of ATP binding and/or hydrolysis at these sites by two complementary approches is in progress. The first approach is to study the kinetics of the nucleotide hydrolysis and nuclease reactions as a function of the type and concentration of nucleotide and DNA substrates. The development of enzyme assay methods allows an examination of several facets of these reactions. In addition, individual amino acids in each subunit which are thought to be directly involved in ATP binding have been identified. Several of these amino acids have been altered by site-directed mutagenesis techniques. The enzymatic properties of the mutant enzymes compared to those of the wild-type using the assay methods alluded to above are also under investigation.
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