Intracellular andExtracellular Cyclic Nucleotides inWild-Type andWhiteCollar Mutant Strains ofNeurospora crassa TEMPERATUREDEPENDENTEFFLUXOF CYCLICAMP FROM MYCELIA

Cyclic AMP andcyclic GMP werereleased into thegrowth medium ofmycelia ofNeurospora crassa wild-type strains St.L.74A andEm5297a andbywhite collar-i andwhite collar-2 mutant strains. After growth for 6days at18°C, there were2.19 (St.L.74A), 5.83 (Em5297a), 1.38 (white collar-i), and1.10 (white collar-2) nanomoles ofcyclic AMP pergram dryweight ofmycelia inthegrowth medium. These values corresponded toconcentrations ofcyclic AMP ofbetween approximately 10and50 nanomolar. Thecorresponding values forextracellular cyclic GMP were typically less than6%ofthevalues forcyclic AMP.Following transfer tofresh medium, cyclic AMP efflux wasdemonstrated foreachofthe strains, andtheamountofcyclic AMP exported into thefresh medium wasgreater at25°Cthan6°C. Intracellular cyclic AMP andcyclic GMP werealso measured ineachofthestrains. Thevalues forcyclic AMP wereinthesamerange asthose intheliterature (approximately 0.5to 1.5nanomoles pergramdryweight ofmycelia). However, thecorrespondingintracellular cyclic GMP values wereless than1%ofthecyclic AMP values, i.e. morethan50times lower thanthevalue previously reported fortheSt.L.74A wild-type. Transfer ofmycelia after 6days at18°C to fresh media andincubation for 2hours at25°C or6°Cdidnotconsistently affect theintracellular level ofcyclic AMP orcyclic GMP inthestrains examined. Wecould detect nochange inintracellular cyclic AMP when mycelia oftheSt.L.74A wild-type strain wereirradiated with bluelight forperiods ofupto3.0hours at180C,orincyclic AMP andcyclic GMP forirradiation times ofupto1minute at6°C. We propose thatthe plasma membrane ofNeurospora crassa ispermeable tocyclic nucleotides, andtheexport ofcyclic nucleotides into thegrowth medium may beameansofregulating intracellular levels. We conclude thatthree factors thataffect carotenogenesis inNeurospora crassa (blue light, temperature, andthewhite collar mutations) havenoappreciable effect onthetotal measurable intracellular cyclic nucleotides inthis organism. There wasnoextracellular orintracellular cyclic AMP orcyclic GMP inthecrisp-i mutant strain, which suggested either that adenylate cyclase (which isabsent incnisp-i) catalyzes thesynthesis ofbothcyclic AMP andcyclic GMP orthatthecnisp-i mutation somehowresults ina deficiency oftwoenzymes (adenylate andguanylate cyclase).