Thursday, September 13, 2012

One more GTPase that binds ppGpp: RF3

The stringent response alarmone ppGpp is very, very similar to GDP: add two more phosphates and you have it... So it is only natural that GTPases mistake the two.

Now Kihira and collegues has added one more to the list - bacterial termination factor 3, RF3. This factor is involved in release of the class one release factors, RF1 and RF2. It binds to the ribosome in the GDP-bound state, exchanges GDP to GTP and kicks the class 1 factors offppGpp:RF3 complex is not as active as GDP:RF3 one, a situation similar to that with initiation factor 2, IF2

The question is is it a specific regulatory mechanism or are GTPases just promiscuous enough? After all, even archael elongation factor 1A, aEF1A, is inhibited by ppGpp as well. And these two never meet in nature...

Kanjee and collegues have recently compiled a list of proteins that ppGpp binds to... or is expected to bind to. GTPases are there, as a whole class of enzymes.


Kihira et al. FEBS J. (2012) in press

Kanjee et al. Mol. Microbiology (2012): 85 (6) 1029-1043 PIMD: 22812515

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