CLONING AND SEQUENCING OF CDNA OF THE INSECTICIDAL TOXIN HIRSUTELLIN-A

The hyphomycete Hirsutella thompsonii produces an extracellular insect icidal protein, Hirsutellin A. This basic protein, cytolytic against i nsect cells and capable of inhibiting protein translation, possesses b iological features similar to the well-characterized ribosomal-inhibit ing proteins (RIPs) alpha-sarcin, mitogellin, and restrictocin. Clonin g and DNA sequencing analysis of the 3' and 5' RACE products of HtA cD NA 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 M-r = 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 RI Ps. (C) 1998 Academic Press.