why tac promoter?

Neil Saunders saunders at bio.vu.nl
Mon Nov 29 16:04:51 EST 1999

Muhammad Abdullahi <daniboyton at my-deja.com> wrote in message
news:81ug6m$srt$1 at nnrp1.deja.com...
> Question (1)In a plasmid, what makes a "tac" promoter more effective
> than any other promoter, and why?
> Question (2)also, can anyone explain in detail, or something to that
> efect, the significance of a plasmid having a high copy number.

(1) The tac promoter, a hybrid of 2 strong promoters (trp and lac)  is
effective because it corresponds to the E. coli consensus -10 and -35
sequences, tataat and ttgaca.  In natural promoters this is only a consensus
which rarely if ever found.

(2) Not sure what you mean by "significance".  The gene products of high
copy number plasmids will obviously be present at higher concentrations.  If
you mean "how is it controlled", the number depends mainly on the levels of
Rep proteins, which bind and initiate replication.

Neil Saunders

Department of Molecular Cell Physiology,
Faculty of Biology,
Vrije Universiteit,
De Boelelaan 1087,
1081HV, Amsterdam,
The Netherlands

tel: +31 20 4447194
fax: +31 20 4447229

email: saunders at bio.vu.nl

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