Jason gile giles at eburg.com
Tue Mar 5 13:20:11 EST 1996

Hi, thanks for taking a look!!  Here is the question 
---Expression of a critical gene regulatory protein can trigger
expression of a whole battery of downstream genes.  A downstream gene
is a gene whose expression is affected by the expression of a
regulatory protein.  Such is usuallly the case in celllular
differentiation.  For example, certain fibroblasts strain (A7) can be
converted into muscle cells by expressing the myoD gene.  In this case
the fibroblasts already express the myogenic genes Myf5 and myogenin.
Myogenic genes encode regulatory proteins that activate the
transcription of muscle-cell specific genes (ie. genes fo the muscle
cell proteins:  myosin, actin, tropomyosin, creatine phosphokinase,
etc.)  Fibriblasts that are not expressing Myf5 and myogenin genes
(strains other than A7) will require that these regulatory proteins be
expressed as well as MyoD for differentiation  to occur.  Given that
these cells no longer divide once differentiated, explain how this
differentiation occurs by

           A) discussing the probable means of transcriptional
activation of the muscle-cell specific genes, and 
           B)  postulating a means by which myoD epression might
ultimately  signal cell cycle arrest.

         (Hint:  in order for some enhancers to function they will
require the binding of two or more different regulatory proteins.)
      Please send responses to Giles at eburg.com   
  YOUR HELP IS APPRECIATED -------------thanks,  Jason

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