From: Dr A.J. Rowe <ajr@leicester.ac.uk>
  To  : Arturo J. Morales <art@scripps.edu>
  Date: Tue, 5 Jan 1999 18:08:04 +0000 (GMT)

Re: Interesting problem...

Art -

There are some puzzling features about your data. As John Philo as said, how are
you calculating M from s + vbar ?  On the assumption that all species
under consideration are more or less globular (bit dodgy for tRNA) then the Squi
re Himmel equations can be used to estimate M values. From your data, these com
out as:

RNA		s = 3.0S	vbar = 0.53	M = 14823	+/-978

Protein		s = 2.0S	vbar = 0.7595	M = 21923	+/-1447

So, whilst I agree that your M value for the protein does not differ
significantly from that expected (24 kD), the RNA estimate is wildly out as
compared to tRNA. And whilst correcting for asymmetry would be a step in the
right direction, its just not a big enough effect in this case.

Just a thought - are you by any chance using RNA in unbufferd aqueous solution ?
If so, the s value might be too low, even at low solute concentration because of
charge effect.

IN PRINCIPLE it ought to be possible to work out the stoichiometry from s values
alone, since there are only a very small number of real possibilities (1:1, 1:2,
2:1, 2:2 ?). You just work out the s value for each, using an appropriately
weighted vbar and the Squire-Himmel equations. And see which estimate fits.
However, that is only valid if you get the right M for each individual species,
and you do not.

A further complication. There is no plausible way in which a 2S species can
combine with a 3S species to give a 2.5-2.8 S complex, even at 1:1. Well, short
of wildly improbably huge unfolding of a component on association. 

Can you tell us how you are determining your s values ?  That might help a lot.

All very best

Arthur

***************************************************
	Arthur J Rowe
	Professor of Biomolecular Technology 
	University of Nottingham
	The NCMH Business Centre
	School of Biological Sciences	
	Sutton Bonington
	Leicestershire LE12 5RD,  UK:
 
	Tel/voicemail	: +44 (0)115 951 6156
	Tel/Fax		: +44 (0)115 951 6157
	arthur.rowe@nottingham.ac.uk}
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