Kinetics of transcription of infectious laryngotracheitis virus genes

The kinetics of expression of only a few genes of infectious laryngotracheitis virus (ILTV) have been determined, using northern blot analysis. We used quantitative reverse transcriptase PCR to examine the kinetics of expression of 74 ILTV genes in LMH cells. ICP4 was the only gene fully expressed in the presence of cycloheximide, and thus classified as immediate-early. The genes most highly expressed early in infection, and thus classified as early, included UL1 (gL), UL2, UL3, UL4, UL5, UL6, UL7, UL8, UL13, UL14, UL19, UL20, UL23 (TK), UL25, UL28, UL29, UL31, UL33, UL34, UL38, UL39, UL40, UL42, UL43, UL44 (gC), UL47, UL48 (α-TIF), UL49, UL54 (ICP27), US3 and US10. ORF A, ORF B, ORF C, ORF E, sORF 4/3, UL[−1], UL0, UL3.5, UL9, UL10 (gM), UL11, UL15a, UL15b, UL18, UL22 (gH), UL24, UL26, UL30, UL32, UL36, UL45, UL49.5 (gN), UL52, US2, US4 (gG), US5 (gJ) and US9 were most highly expressed late in infection and were thus considered late genes. Several genes, including ORF D, UL12, UL17, UL21, UL27 (gB), UL35, UL37, UL41, UL46, UL50, UL51, UL53 (gK), US8 (gE), US6 (gD) and US7 (gI), had features of both early and late genes and were classified as early/late. Our findings suggest transcription from most of ILTV genes is leaky or subject to more complex patterns of regulation than those classically described for herpesviruses. This is the first study examining global expression of ILTV genes and the data provide a basis for future investigations of the pathogenesis of infection with ILTV.