Infectious Laryngotracheitis Herpesvirus Expresses a Related Pair of Unique Nuclear Proteins Which Are Encoded by Split Genes Located at the Right End of the U_LGenome Region

Abstract

Avian infectious laryngotracheitis virus (ILTV) possesses an alphaherpesvirus type D DNA genome of ca. 155 kbp. Completion of our previous sequence analyses (W. Fuchs and T. C. Mettenleiter, J. Gen. Virol. 77:2221–2229, 1996) of the right end of the unique long (UL) genome region revealed the presence of two adjacent, presumably ILTV-specific genes, which were named UL0 and UL[−1] because of their location upstream of the conserved UL1 (glycoprotein L) gene. Transcriptional analyses showed that both genes are abundantly expressed during the late phase of the viral replication cycle and that both mRNAs are spliced by the removal of short introns close to their 5′ ends. Furthermore, the deduced gene products exhibit a moderate but significant homology of 28% to each other. The newly identified ILTV genes encode proteins of 63 kDa (UL0) and 73 kDa (UL[−1]), which both are predominantly localized in the nuclei of virus infected chicken cells. In summary, our results indicate that duplication of a spliced ILTV-specific gene encoding a nuclear protein has occurred during evolution of ILTV.

Deletion of the non-essential UL0 gene of infectious laryngotracheitis (ILT) virus leads to attenuation in chickens, and UL0 mutants expressing influenza virus haemagglutinin (H7) protect against ILT and fowl plague

“…Construction of UL0 deletion plasmids and ILTV recombinants. Plasmid pILT-E43, which contains an 11?2 kbp EcoRI fragment of the ILTV genome (Ziemann et al, 1998b), was shortened by consecutive HindIII/BstXI and EcoRI/XhoI double digestions and re-ligations. As in subsequent experiments, non-compatible, singlestranded overhangs of digested DNA were polished by treatment with Klenow polymerase prior to ligation.…”

“…In contrast, the products of the ILTVspecific UL0 and UL [21] genes at the right end of the U L region (Fig. 1) accumulate in the nuclei of infected cells (Ziemann et al, 1998b). The common localization of the UL0 and UL [21] proteins correlates with similar gene structures, since both ORFs contain small introns within their 59-terminal parts, which are removed by mRNA splicing (Ziemann et al, 1998b).…”

“…Recently, we demonstrated that in infected chicken cell cultures, seven of these ILTV-specific genes are indeed transcribed and translated into proteins (Veits et al, 2003b;Ziemann et al, 1998b). The protein products of a cluster consisting of five ORFs (A-E) located downstream of UL22 were detected predominantly in the host cell cytoplasm (Veits et al, 2003b).…”

“…1) accumulate in the nuclei of infected cells (Ziemann et al, 1998b). The common localization of the UL0 and UL [21] proteins correlates with similar gene structures, since both ORFs contain small introns within their 59-terminal parts, which are removed by mRNA splicing (Ziemann et al, 1998b). Furthermore, UL0 and UL[21] exhibit a significant amino acid sequence homology of 28 %, indicating that the two genes presumably originated from an ancient duplication event (Ziemann et al, 1998b).…”

“…The common localization of the UL0 and UL [21] proteins correlates with similar gene structures, since both ORFs contain small introns within their 59-terminal parts, which are removed by mRNA splicing (Ziemann et al, 1998b). Furthermore, UL0 and UL[21] exhibit a significant amino acid sequence homology of 28 %, indicating that the two genes presumably originated from an ancient duplication event (Ziemann et al, 1998b). By construction of genetically engineered virus recombinants, we demonstrated that the ILTVspecific ORF A-E genes are dispensable for virus replication in cultured cells and speculated that these genes might be relevant only during infection of chickens (Veits et al, 2003b).…”