Primase (dna G)
E.coli DNA Primase (dna G) was discovered in 1972 by K. G. Lark. Kasper
Zechel, Jean-Pierre Bouche and Arthur Kornberg pushed this discovery further
when they uncovered the function of dna G through the use of two phage strains
and the wild-type E.coli uninfected. The phage strains were G4, and G14. They
assayed the modified E.coli for RNA polymerase activity. Zechel et al reported
the procedures and results in a paper in 1975 published in The Journal of
Biological Chemisty (pp.4684-4689).
The dna G protein works as part of a multi-enzyme complex with dna B in order to
prime the strands of DNA. Dna G seeks out a 3'- GTC sequence and adds on the
primer about 11 nucleotides3. This complex is known as a "primosome." The
primosome stimulates primer synthesis by RNA polymerase. The primosome
continually moves along the lagging strand in order to prime each Okazaki
fragment, and only primes once on the leading strand. Okazaki is credited with
the discovery of much of these facts because of his studies of DNA replication
which lead him to his conclusion of a semidiscontinuous mechanism.
The images above and below are of Primase in a cartoon representation at
different angles.
Helical segments of the protein are shown in blue and beta sheet regions are
shown in red.
The above image is of Primase in a spacefilling representation in order to more
easily see the three dimensional features of the compound.
Helical segments of the protein are shown in blue and beta sheet regions are
shown in red.
References:
Zechel, K et al. (1975) The Journal of Biological Chemistry. 250, pp. 4684-4689
Kornberg, A and Baker, T. (1992) DNA Replication. (Ed. 2). Pp.282-283
Weaver, R. F. (1999) Molecular Biology. Pp.666
Lark, K. G. (1972) Nature New Biology. 240, pp.237-240