26 Flashcards
(35 cards)
default expression of trp
ON- repressor is present but functionally inactive)
what happens when supply of trp is sufficient
expression needs to be turned down or off- repressor must become functionally active
strength of trp operon promoter
is strong
what turns trp promoter off
repressor whose functionality/ activity depends on [trp]
what is the corepressor
trp
what kind of system is trp
repressible system
layout of the genes for trp
there are five
located together
regulataed together as an operon
trp genes when trp is in short supply
must all be expressed- operon ON- repressor does not bind to operator- bc of repressor
trp genes when trp is abundant
genes do not need to be expresed- operon OFF- repressor binds to operator- repressor and trp
trp repressor structure
helix turn helix DNA binding protein whose functionality depends on the level of trp in th ecell
not positioned correctly for binding to DNA in the native protein
where does trp bind
to each trp repressor monomer and changes the conformation so that the DNA binding helixes are then positioned correctly
where does the trp repressor bind
only to DNA when it itself is bound by trp and that only happens when trp levels are high
when trp levels are high
trp repressor binds with trp enabling repressor to bind to its operator and prventing RNA pol from transcribing from the trp promoter
in absence of trp
trp repressor does not bind to DNA and RNA pol can bind to the trp promoter to express the genes thereby leading to trp biosynthesis
where are the genes that encode the regulator protein- trp repressor located
elsewhere in the genome and is transcribed independently and translated
trpR-
non functional repressor mutant
delta trpR
the trpR gene has been deleted and can never make any type of TrpR protein
trpR- cell
produces trp
operon is intact
strong promoter
nothing preventing wild type levels of trancrption and expression
trp added to trpR- cells
repressed by trp
therefore the trp operon is subject to a second level of control that involves monitoring of the [trp]
Are there mutants of the trpR- mutatnts that do not show this second level of trp sensitivitty
trp operon expression in trpR- mutatns is increasd by mutation in
trp-tRNA synthetase (trpRS) gene- trpS
the tRNAtrp gene- trpT
genes whose porducts modify tRNAtrp
what is involved in trp operon control
tRNAtrp
also at the level of translation- due to formation of alternative RNA structures in the mRNA which lead to attenuation of transcription
what does trpL encode for
a short peptide that contains two WW
translation of the leader peptide mRNA is sensitive to
trp-tRNAtrp conc which of course relfects the trp concentration
what determines whether the rest of the peptide is transcribed
timely translaiton of the leader peptide
