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  From: Jo Butler <>
  To  :
  Date: Thu, 17 Sep 98 09:57:52 +0000

Re: vbar for RNA-Protein complex?

>Date: Wed, 16 Sep 1998 14:58:21 -0700
>From: "Arturo J. Morales" <>
>Subject: vbar for RNA-Protein complex?
>As usual, we are trying to do something we dont have much experience on :)
>I have a likely RNA-Protein complex, but haven't found to way to calculate
>a vbar for it from sequence... can anyone give me a quick pointer to where
>I could find such info?  Is this a viable thing to do? are there any other
>preffered methods to look calculate MW of a complex in the AU?
>Here's the system:
>We have a farily invisible protein (No Trp's,  2Tyr, 2Phe)... and it seems
>to interact with an RNA... By following the ABS at 260nm, and calculating
>the MW in an eq. reaction, we should get good data (in a perfect world, of
>course)... I expect vbar to change from that of a pure RNA to somewhere in
>between an RNA and the protein, but I'm not sure how to approach this...
>Thanks in advance!
>     Arturo J. Morales    (RPI
>   Department of Biology - Massachusetts Institute of Technology &
>  Skaggs Institute for Chemical Biology - Scripps Research Institute

Dear Art,

A reasonable approximation (as good as any calculated value for v-bar) is
by applying the usual equation (summing v-bar * M and dividing by the sum
of M),
as you would do with an amino acid composition for a protein.

The error in any such calculation arises from interactions between the
components which change their aggregate volumes.  I do not know of any way
solving this except, of course, for measuring the apparent v-bar

Yours sincerely,


Jo Butler, 
Cambridge, UK.
Tel:+44 1223 248011
FAX:+44 1223 213556

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