are there any proteins < 1 kD?

Vladimir Svetlov svetlov at
Sat Nov 22 18:30:06 EST 1997

In article <657av7$cao$1 at>,
mlevin at (Michael Levin) wrote:

>    Are there any proteins or protein families less than 1 kD in size? I'm
> especially interested in ones which may have an interesting role in some
> process (regulation, development, etc.). Please send any ideas to
> mlevin at (or, if there's some database that one can search
> with this sort of criteria in mind, I'd be very grateful to know). 
> Thanks!
> Mike Levin

The term proteins is usually applies to large (=high molecular weight)
peptides, produced ribosomally and as a rule with a compact water-soluble
state (aka folded protein). A "protein" <1 kD in size should be a peptide
<9 amino acids long. Such peptides can be produced ribosomally (see ORFs
upstream of yeast GCN4) but they can not be called proteins. Depending on
the origin such peptides may even form a "family", but I must admit my
total ignorance of such parsimonies. Non-ribosomal peptides of this size
play role in many signal transduction phenomena, but they can't be called
"proteins" either.\

Vladimir Svetlov
McArdle Lab for Cancer Research
Dept. Oncology
1400 University Ave.
Madison, WI 53706

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