Characterization of DNA-binding proteins and protein kinase activities in Chlorella virus CVK2

Several capsid proteins were selectively released from the viral core of Chlorella virus CVK2 by treatment with 4M urea. Among the viral core proteins, seven species (Vp154, Vp73, Vp63, Vp52, Vp48, Vp42, and Vp25) were shown to have DNA-binding activities by Southwestern blot analysis. Except for Vp154 and Vp25, these DNA-binding proteins showed a specific affinity for the viral genomic DNA. The viral core also contained three proteins with protein kinase activity (Vp73, Vp60, and Vp37); Vp73 seemed to have both DNA-binding and protein kinase activities. Antisera raised against Vp73 were used to screen a lambda-CVK2 expression library for the gene encoding Vp73. Three different clones (Vp73-3, Vp73-29, and Vp73-42) were obtained and analyzed. ORFs found in these clones all contained characteristic proline-rich motifs. The Vp73-42 ORF showed a strong similarity with histone H1 of various organisms and the Vp73-29 ORF contained two regions with leucine-zipper motifs. All three genes were expressed late in infection.