determining oligomeric structure of a protein

[Roland J Saldanha]

I am working on the mitochondrial tyrosyl synthetase that functions as both a 
synthetase and as a facilitator of group I intron splicing.  In characterizing 
the protein we find that it elutes from gel filtration columns with an apparent
molecular weight of a tetramer (monomer MW=72,000).  However the protein 
crosslinks as a dimer with dimethyl suberimidate and glutaraldehyde.  This 
would suggest a highly elongated structure that has an aberrant mobility 
(reflecting the elongated size) in gel filtration.
I would welcome suggestions for other methods for demonstrating the oligomeric 
structure of the protein.  I am aware that sedimentation analysis is the best 
method of approaching this problem but do not have access to an analytical 
ultracentrifuge and would welcome collaborative offers from anyone who has a 
machine.
We would also like to try native page but the protein is very basic (computer 
calculated pI of 10.3).  I would thus welcome suggestions for native gels of 
basic proteins and suitable standards for basic proteins.