protein deletions

Sat Oct 12 19:47:53 EST 1991

 Typically, proteins cannot tolerate deletions in their central regions
of more than a single amino acid. Frequently, however, part of the
c-terminal portion of the protein can be cut off. In many of these cases
I think that a second,nonassayed function is being removed. An example
is our work on lac repressor. We have tried making deletions between
5-60 amino acids in various portions of the protein. You can't delete
between psns 1-330, but positions 330-360 can be cut off. It turns
out this region allows the dimers to tetramerize, and contains a
probable mini leucine zipper. The tetramer can bind two DNA sequences at
once which slightly improves repression, but the dimer is almost as
good. We didn't realize the effect until we tried gel retardation. 
So to summarize, c-terminal regions may contain removable "optimizing"
portions of protein function.
-Peter Markewicz

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