Delaroque N., Mueller D.G., Maier I., and Knippers R.
Fakultaet fuer Biologie der Universitaet, D-78457 Konstanz, Germany.
The marine brown alga Ectocarpus siliculosus is frequently infected by a virus that multiplies in modified gametangia and sporangia of the host. EsV particles are characterized by an icosahedral multilayered capsid enclosing a circular double stranded DNA of about 320 kb which is interrupted by single-stranded regions. Based upon one-dimensional SDS-PAGE analysis, the virus contains at least 50 proteins ranging in molecular mass from 20 to > 100 kDa, one of which is the glycoprotein gp-1. In an attempt to better understand the molecular aspects of the EsV infection cycle we have focused our investigations on structural proteins and the state of viral DNA during the latent phase. Several capsid proteins were identified by immunological screening of a ZAP Express expression library of EsV DNA with an antiserum raised to structural proteins. The corresponding genes were partially sequenced and mapped by Southern blots. Computer-assisted search did not reveal homologies to known protein virus sequences, supporting the idea that brown algal viruses are a phylogenetically distinct group. Furthermore, we are now able to isolate high molecular alga DNA by pulsed-field agarose electrophoresis. Polymerase chain reaction with virus specific primers confirms the integration of the viral DNA in the host genome.