Locus-Specific Gene Expression Pattern Suggests a Unique Propagation Strategy for a Giant Algal Virus

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Emiliania huxleyi</jats:italic> virus strain 86 is the largest algal virus sequenced to date and is unique among the <jats:italic>Phycodnaviridae</jats:italic> since its genome is predicted to contain six RNA polymerase subunit genes. We have used a virus microarray to profile the temporal transcription strategy of this unusual virus during infection. There are two distinct transcription phases to the infection process. The primary phase is dominated by a group of coding sequences (CDSs) expressed by 1 h postinfection that are localized to a subregion of the genome. The CDS of the primary group have no database homologues, and each is associated with a unique promoter element. The remainder of the CDSs are expressed in a secondary phase between 2 and 4 hours postinfection. Compartmentalized transcription of the two distinctive phases is discussed. We hypothesize that immediately after infection the nucleic acid of the virus targets the host nucleus, where primary-phase genes are transcribed by host RNA polymerase which recognizes the viral promoter. Secondary-phase transcription may then be conducted in the cytoplasm. </jats:p>