Cloning and sequencing of cDNA of the insecticidal toxin hirsutellin A

The hyphomycete Hirsutella thompsonii produces an extracellular insecticidal protein, Hirsutellin A. This basic protein, cytolytic against insect cells and capable of inhibiting protein translation, possesses biological features similar to the well-characterized ribosomal-inhibiting proteins (RIPs) alpha-sarcin, mitogellin, and restrictocin. Cloning and DNA sequencing analysis of the 3' and 5' RACE products of HtA cDNA identifies a consensus DNA sequence which encompasses the complete open reading frame of the HtA gene. This gene codes for a precursor of 164 aa which includes a 34-aa leader sequence. The leader sequence of HtA, like those found in RIPs, contains a signal and a pro sequence. The mature 130-aa HtA, having a calculated Mr = 14,159 and pI = 9.21, is considered a stable hydrophilic protein. HtA does not possess the characteristic RNase motif of fungal RIPs but does possess a series of consensus phosphorylation and myristoylation sites and a putative ATP/GTP binding site. The sequence of HtA is unique and does not produce the secondary or tertiary structures characteristic of other fungal RIPs. Copyright 1998 Academic Press.