The development of perithecia in Neurospora crassa is under the control of light, nutritional condition such as nitrogen starvation and temperature. Blue light can stimulate(i)the formation of protoperithecia on nitrogen deficient media, (ii)positive bending of perithecial beak, and(iii)the ejection of ascospores from asci in the perithecia. We found that the position of the formation of perithecial beak was dependent on light.(iv)Light stimulated the positioning of perithecial beak on the upperward of it, which we defined as“ light induced polarity of perithecia”. We developed in vitro systems to analyse molecular mechanism of light signal transduction that used the membrane and soluble fractions of mycelial extract. UV-A light induced the binding of ATP/GTP to 58kDA, 77kDa, 83kDa, and 129kDa proteins in the membrane fraction. Blue light stimulated the ADP-ribosylation of 38kDa and 56kDa proteins in the soluble fraction. Blue light also stimulated the phosphorylation of 15kDa protein in the membrane fraction. We isolated a mutant missing completely the phosphorylation of 15kDa protein in the membrane fraction. The mutation designated as psp(phosphorylation of small protein)was mapped on LGVR between al-3and his-6. The psp mutats showed blindness in the light induced polarity of perithecia. The 15kDa protein was purified and the cDNA was cloned. It was identified as nucleoside diphosphate(NDP)kinase. The cDNA for NDP kinase prepared from psp mutants included a mutation of amino acid replacement from Pro 72to His. The putative function of NDP kinase in the light signal transduction to perithecial morphogenesis was discussed.