Diguanosine nucleotides of fungi that regulate RNA polymerases isolated and partially characterised.

Three unusual phosphorylated diguanosine compounds called ‘hot spots’ HS-1, HS-2 and HS-3 (ref. LéJohn, H.B. Proc. Can. Fed. Biol. Soc. 18, 159, 1975) have been isolated as acid-soluble materials from several fungi, $\text{Achlya, Blastocladiella emersonii, Aspergillus niger}$ and $\text{Rhizopus stolonifer}$ in their vegetative phase. The nucleotides were purified from acid extracts of $\text{Achlya}$ and $\text{Blastocladiella}$. The tentative structures of HS-3 and HS-2 determined are GppppG and GppppGp. HS-1 structure is still in doubt but it is related to HS-2. The structures were deduced from enzymatic digestion and UV analyses of the products, molar ratios of guanosine and phosphate, and chromatographic behaviour on PEI-cellulose. All three compounds accumulated in an inverse manner with rates of RNA synthesis and directly with rates of protein synthesis. The acid-soluble pools of the three compounds fluctuated during the life cycle of $\text{Achlya}$, and just prior to sporulation, were excreted into the medium. HS-2 was convertible to HS-3 by acid hydrolysis.