Co-expression offers an important strategy for producing multiprotein complexes 
for biochemical and biophysical studies. We have found that co-expression of 
histones H2A and H2B (from yeast, chicken or Drosophila) leads to production of 
soluble heterodimeric H2AH2B complexes. Drosophila histones H3 and H4 can also 
be produced as a soluble (H3H4)(2) heterotetrameric complex if they are 
co-expressed with the histone chaperone Asf1. The soluble H2AH2B and (H3H4)(2) 
can be purified by simple chromatographic techniques and have similar properties 
to endogenous histones. Our methods should facilitate histone production for 
studies of chromatin structure and regulatory proteins that interact with 
histones. We describe a simple strategy for constructing co-expression plasmids, 
based on the T7 RNA polymerase system, which is applicable to other systems. It 
offers several advantages for quickly creating plasmids to express two or more 
proteins and for testing different combinations of proteins for optimal complex 
production, solubility or activity.