NUCLEOTIDE AND DEDUCED AMINO-ACID-SEQUENCES OF THE NUCLEOCAPSID PROTEIN OF THE VIRULENT A75 17-CDV STRAIN OF CANINE-DISTEMPER VIRUS/

Virus persistence is essential in the chronic inflammatory canine dist emper virus (CDV)-induced demyelinating disease. In the case of CDV th ere is a close association between persistence and virulence. Virulent CDV isolated from dogs with distemper shows immediate persistence in primary dog brain cell cultures (DBCC) and in different cell lines. We have evidence that the nucleocapsid (NP) protein plays an important r ole in the development of persistence. The NP-protein, the most abunda nt structural virus protein, also influences virus assembly and has so me regulatory functions in virus transcription and replication. In thi s study we compared the nucleotide and deduced amino acid sequence of a virulent CDV strain (A75/17-CDV) to a culture-attenuated non-virulen t strain (OP-CDV). Viral RNA was extracted from DBCC infected with vir ulent CDV. Virulent CDV retains its in vivo properties, such as virule nce and ability to cause demyelination, when propagated in these DBCC. The viral RNA was reverse transcribed and the resulting cDNA amplifie d by polymerase chain reaction for subsequent cloning. The nucleotide sequences of these clones were determined by the dideoxy chain termina tion method. The number of nucleotides and the putative NP-protein of the virulent strain matched the attenuated CDV strain. We observed a t otal of 105 nucleotide differences. Three were localised within the 3' and five within the 5' non-coding region of the NP-gene. The 97 nucle otide changes within the coding region resulted in 22 amino acid diffe rences. 10 of these amino acid (AA) modifications were within the N-te rminal region (AA 1 to 159) and 12 within the C-terminal area (AA 351 to 523). These regions flanked a highly conserved middle region (AA 16 0 to 350). No amino acid differences were found within the middle area of the CDV NP-protein. The secondary structure prediction of the A75/ 17-CDV NP-protein at the C-terminus resulted in obvious differences fr om OP-CDV. The present study provides a plausible molecular basis for the differences between a cytolytic and a persistent CDV-infection.