Abstract
Histone H3-lysine9 (H3K9) trimethyltransferase gene Su(var) 3-9 was cloned and identified in three Spodoptera insects, Spodoptera frugiperda ( S . frugiperda ), S . exigua and S . litura . Sequence analysis showed that Spodoptera Su(var) 3-9 is highly conserved evolutionarily. Su(var) 3-9 protein was found to be localized in the nucleus in Sf9 cells, and interact with histone H3, and the heterochromatin protein 1a (HP1a) and HP1b. A dose-dependent enzymatic activity was found at both 27 °C and 37 °C in vitro, with higher activity at 27 °C. Addition of specific inhibitor chaetocin resulted in decreased histone methylation level and host chromatin relaxation. In contrast, overexpression of Su(var) 3-9 caused increased histone methylation level and cellular genome compaction. In AcMNV-infected Sf9 cells, the transcription of Su(var) 3-9 increased at late time of infection, although the mRNA levels of most cellular genes decreased. Pre-treatment of Sf9 cells with chaetocin speeded up viral DNA replication, and increased the transcription level of a variety of virus genes, whereas in Sf9 cells pre-transformed with Su(var) 3-9 expression vector, viral DNA replication slow down slightly. These findings suggest that Su(var) 3-9 might participate in the viral genes expression an genome replication repression during AcMNPV infection. It provided a new insight for the understanding virus–host interaction mechanism.
Highlights
Post-translational modifications on N-terminus of core histones, such as methylation, acetylation, phosphorylation, ubiquitination and glycosylation, etc., could affect the affinity between histones, DNA and a variety of protein factors, and change the status of chromatin compaction and gene expression [1,2]
It was verified by polymerase chain reaction (PCR) with Complementary DNA (cDNA) as template
The polyadenylation signals (AAUAAA) downstream of each Open reading frames (ORFs) are found in the genomic sequence
Summary
Post-translational modifications on N-terminus of core histones, such as methylation, acetylation, phosphorylation, ubiquitination and glycosylation, etc., could affect the affinity between histones, DNA and a variety of protein factors, and change the status of chromatin compaction and gene expression [1,2]. Site- and state-specific methylations of histone Lysine or Arginine are catalyzed by a family of proteins containing SET domain, which was first identified in Drosophila Su(var) 3-9, Enhancer of zeste and Trithorax [3], from which the acronym is derived. The Cterminal half of SET contains H(x2) NHSC and GE(x5) Y motifs, which was defined as the catalytic core [4,5]. It is often flanked by one or both of the functionally associated domains named preSET and postSET [3,4]. Different histone Lysine methyltransferases (HLMTs) have variable activities to catalyze Lysine methylations at different site (H1K26, H3K4, H3K9, H3K27, H3K36, H3K79 and H4K20), and to different methylation statuses (mono-, di- and trimethylation)
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