Structural Characterization and Expression Analysis of the Neurospora Conidiation Gene con-6

Abstract

The gene con-6 of Neurospora crassa is expressed during the formation of asexual spores (conidia), but it is not expressed in mycelium. con-6 mRNA appears upon induction of conidiation and reaches high levels at the late stages of conidiation, and in mature conidia. The CON6 polypeptide and a CON6-βGal fusion protein were present at high levels only in free conidia. Shortly after spore germination con-6 mRNA disappears and the CON6 polypeptide is degraded. CON6 is a small, hydrophilic polypeptide containing a repeat sequence; it not homologous to any known protein but has features resembling the late embryogenesis abundant proteins of maize. Inactivation of con-6 by the repeat-induced point mutation process had no demonstrable effect on formation or germination of conidia. Upstream sequence comparisons for con-6 and other con genes identified a common potential regulatory sequence, designated CRS-B. DNA mobility shift analyses with cell extracts identified a factor that bound to synthetic DNA fragments containing this sequence. This binding factor was present in mycelium but not in conidiating cultures. Experiments with independent integrated con-6′-'lacZ translational fusions revealed substantial variability of expression among transformants carrying identical fusion constructs. This variability may be due to the differential methylation of transformant DNA noted by others.