Viktoriya Shyp "G nucleotide regulation of translational GTPases and the stringent response factor RelA"

Supervisors: prof. Tanel Tenson ja Vasili Hauryliuk (Tartu Ülikool)

Opponent: Michael Cashel, National Institute of Health, USA

Summary:
G nucleotides - GTP, GDP, and the stringent alarmon ppGpp - significantly affect bacterial translation. In frame of this work we studied ppGpp synthesis and translational GTPases regulation mechanisms. The level of ppGpp changes during the stress conditions, particularly under nutrients deprivation. In this work, we have shown that ppGpp stimulates its own RelA-mediated synthesis. Such positive feedback regulation provides a mechanism of quick response to stress. It was suggested previously that ppGpp inhibits several ribosome-associated translational factors. However, the primary target was not known. We have determined that initiation factor 2 (IF2), one of the most essential component of bacterial translational machinery, associates tighter with alarmon nucleotide than other translational factors that makes it the main target for ppGpp in translation. We have determined that the G-nucleotide and initiator tRNA binding events are independent of each other. At the same time, we have shown that GDP affects IF2 and elongation factor G (EF-G) binding to the ribosomal element. Ribosomal RNA fragment from factors binding site associates preferentially with GTP-bound form of these proteins.