AN ABUNDANT HYDROPHOBIN (ABH1) FARMS HYDROPHOBIC RODLET LAYERS IN AGARICUS-BISPORUS FRUITING BODIES

The SDS-insoluble protein fraction of Agaricus bisporus fruiting bodie s was solubilized with trifluoroacetic acid. On SOS-PAGE this fraction was found to contain one abundant protein with an apparent M(r) of 16 kDa. The N-terminal amino acid sequence of this protein was determine d and RT-PCR used to isolate a cDNA clone which upon sequencing identi fied the protein as a typical class I hydrophobin (ABH1). The gene (AB H1) was isolated and sequenced, and a second hydrophobin gene (ABH2) w as found about 2.5 kbp downstream of ABH1. Purified ABH1 self-assemble d at hydrophobic-hydrophilic interfaces, producing the typical rodlet layer known from other hydrophobins. Similar rodlets were observed on the surface of the fruiting body, while immunological localization sho wed the hydrophobin to be particularly abundant at the outer surface o f fruiting bodies, in the veil and in the core tissue of the stipe, Tr anscripts of ABH1 were found only in fruiting-body hyphae. The ABH1 hy drophobin is probably solely responsible for the hydrophobicity of the fruiting-body surface but may also line air channels within fruiting bodies.