TnPhoA mutagenesis question

Rafael Maldonado rafael at
Wed Aug 30 13:37:33 EST 1995

On Tue, 29 Aug 1995 cliff at wrote:
> My question is - does this mean that the fda gene 
> downstream of pgk is automatically inactive (polar mutation) OR does 
> TnphoA (or Tn5 for that matter) have a known endogenous promoter in its 
> inverted repeats ie. will the fda gene be transcribed from within the 
> transposon ? 

Hello Cliff:

Normally, yes. Tn's normally create polar mutations. Some transposons 
have those out promoters, but I think Tn5 does not have any. Any
transponible elements book could give you that information.

Anyway, you may consider internal promoters, very common in some 
operons; even a promoter can be created after the insertion, combining 
sequences from the Tn and the target. Also, polar mutations depends on 
rho-dependent termination spots. So there are some situations when the 
insertions are not polar, but they are pretty infrequent.


Rafael Maldonado                             |  La cita ha sido
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