*MCPs

Dan Jacobson DANJ at JHUHYG.bitnet
Sun Jan 26 22:41:53 EST 1992


In an earlier article Clemens asks:

during a race amplification of plant mRNA, i have stumbled on yet another
gene: this time a sequence with large homologies to proteasome- or "multi-
catalytic proteinases" (MCP)- subunits.
I have been gone through the literature, came up with some interesting
articles, but have still some questions:
1. any news about the functions of MCP ?
2. are MCPs associated with small RNAs (are they snurps)?
3. are they single copy genes ?
4. do you know of other PLANT MCP subunits that were cloned ?
5. do you know of a recent publication (or even review) which discusses
these points ?

I would be gratefull for any useful pointers!

ciao, clemens


###############################################################
# clemens suter-crazzolara    mpi for plantbreeding     koeln #
# tel --49-221-5062.221       fax --49.221.5062.213           #
###############################################################

A while ago I did some reading on these proteasomes/MCPs.

1) Functions:  There have been several theories/implications on the functions
of proteasomes all of course invlved in some sort of protein catabolism.  Perha
ps one of the more interesting is their implication in the ubiquitin-protein ca
tabolism pathway.  The idea is that ubiquitin is attached to certain proteins w
hich are targetd for rapid degradation and the ubiquitin is some sort of tag
that gets these proteins sent down the degradative pathway.  This has been a fi
eld of pretty intense research and there's lot's of literature on the three enz
ymes involved in getting ubiquitin attached to other proteins.  Proteasomes
may be the degradative end of this patway, supposedly chewing up ubiquitinated
proteins quickly.  Proteasomes thmeselves are huge complexes (1000Kd) and
composed of sixteen to twenty distinct subunits.  The proteasome comes in two
or three seperate "parts"  -  the largest of which is called the catalytic core
which contains the actuall protease activities (there are at least three differ
nt types of proteolytic activities in a catalytic core).  The other one or two
"parts" - perhaps better refered to as cofactors - are thought to be neccessary
 for ubiquitin specific degradation of proteins.  The cofactors can be associat
ed and dissociated under different conditions - prehaps implying regulatory con
trol.

2) Association with snRNA snrps etc...:  I believe that ealry assertions that
proteasomes were associated with snRNA, tRNA or were actually snrps has been
discounted as contaminations with snrps or RIBOSOMES as they are all big comple
xes and early purifications were pretty crude.  Note that purifying 1000kd comp
lexes can be pretty tough - especially when it comes to sorting them out from o
ther thins of monsterous size.  Anyway - I don't think that those are presently
thought to be RNA or snrp involved.

3) Single copy genes?  Again these are multi (multi, multi) - subunit complexes
and the cloaning approaches taken so far have often been of the brute force
"get some peptide sequences and then make some oligos approach"  I think 4 or
6 of the subunits had been cloned.  In short there's not enough known yet to
say any or all of the subunit are single or multi-copy genes.

4) Plant MCP/proteasomes cloned? - None that I've heard of.  You could try a fe
w keyword searches on Genbanks IRIX system or PIR's email server.

5) Publications.  There are a few good ones to star with _ -  I'll go into my
office tomorrow and dig them out.
(I'm dialed in from home now, this also explains the less than wonderful typing
job here as none of my editing keys are mapped into the mainframe yet so this
is strictly an asis (as is - see?) job)

Hope this helps,

Dan Jacobson
danj at jhuhyg.sph.jhu.edu



More information about the Bioforum mailing list