Precursor Products Found in Formaldehyde-fixed Lysates of BHK-21 Cells Infected with Pseudorabies Virus

Lysates of BHK-21 cells, infected with pseudorabies and labeled with ³H-thymidine, were treated with formaldehyde and centrifuged in preformed CsCl gradients. Five peaks, designated bands A to E, were detected and shown to contain the following virus-specific products: band A, aggregates of virions; band B, virions; band C, empty capsids and nucleocapsids; bands D and E, small nucleoid-like particles. All five bands contained viral deoxyribonucleic acid and virous-specific antigens. Deoxyribonuclease treatment of the lysates before centrifugation resulted in the complete loss of ³H-thymidine-labeled material from bands D and E; bands B and C were unaffected. Pulse-chase studies showed that ³H-thymidine can be rapidly chased into the virus-specific products sedimenting in bands D and E. Further chase resulted in the gradual loss of label from bands D and E with a concomitant increase in the amount of label in bands A, B, and C. These results indicate that the virus-specific products in bands D and E are precursors of pseudorabies virions and may represent the nucleoid of the virion.