In article <4aqrnh$n44 at saba.info.ucla.edu>, moseley at ewald.mbi.ucla.edu
(Jeffrey Moseley) wrote:
> My question concerns the pausing of the replisome in E. coli during
> co-ordinated leading and lagging strand synthesis. Is due to a lag time in
> synthesis of a new RNA primer on the lagging strand, or is it because of the
> dissociation of the replisome from the lagging strand on encountering the
> 5-prime end of the previous Okazaki fragment?
>
I don't get clearly what you mean for pausing of the replisome. Actually
(as you said) lagging and leading strand DNA synthesis are coordinated, it
means that the new RNA primer is synthesized WHILE the polIII holoenzyme
elongates the previous one. Once the polIII has completed one Okazaki
fragment, it is believed that only the lagging strand, which is looped
around the replisome, transiently dissociate in order to allow polIII to
bind to the new RNA primer. How fast this process is and how it is exactly
coordinated is not precisely known, I guess. The internal asymmetry of the
gamma-complex, anyway, helps the dymeric polIII holoenzyme to be properly
placed at both the leading and lagging strands. Anyway, the dynamic of DNA
replication is far more complex. For example it is not known how recycling
of the beta subunit by the gamma complex to every new primer on the
lagging strand may affect the actual replication rate. In a recent Cell
paper (1994 I guess), O'Donnel at al. measured the rate of recycling in
about 1 sec per loading event, a figure that fits quite well with the rate
of DNA synthesis, thus suggesting that this step is not rate-limiting for
replication. You may be interested in checking also the five papers by
O'Donnel et al. (but he was the last author, not the first), recently
published in JBC (I would say September 1995, I can't recall it now). The
book DNA replication, by Baker T. and Kornberg, A. can give you also a
general view of the process.
Hope it helps. G. Maga.
