Identification and characterization of Piwi subfamily in insects.
As a subfamily of Argonaute proteins, Piwi is poorly understood compared with Ago subfamily until recent discovery of Piwi protein interacting with piRNA. We did a large scale screening of insect genomes to identify piwi-like genes. Full or partial cDNA sequences were obtained by EST elongation and GENSCAN. We found that the exon numbers were totally different between vertebrates and invertebrates, approximately 20 exons in mammals but only 6-9 exons in insects. This infers either intron insertion or loss occurred during evolution. Characterized PAZ, c-terminal PIWI domains exist in almost all predicted Piwi-like proteins. We found six conserved motifs, which contain active catalytic triad "Asp-Asp-His/Lys" required for slicer activity. The expression of siwi1 and siwi2 in Bombyx mori were verified with RT-PCR. Phylogenetic tree inferred by Bayesian algorithm indicates invertebrate Piwi-like proteins are classified into three clades, of which Ago3 clade is closer to mammalian Piwi proteins.
Zhou
Xue
X
Department of Entomology, Nanjing Agricultural University, Nanjing 210095, China; College of Life Sciences, Nanjing Normal University, Nanjing 210097, China.
Liao
Zhen
Z
Department of Entomology, Nanjing Agricultural University, Nanjing 210095, China.
Jia
Qidong
Q
Department of Entomology, Nanjing Agricultural University, Nanjing 210095, China.
Cheng
Luogen
L
College of Life Sciences, Nanjing Normal University, Nanjing 210097, China. Electronic address: chengluogen@njnu.edu.cn.
Li
Fei
F
Department of Entomology, Nanjing Agricultural University, Nanjing 210095, China. Electronic address: lifei@njau.edu.cn.
D000465:Algorithms; D000818:Animals; D000852:Anopheles / Q000378:metabolism; D060565:Argonaute Proteins; D001499:Bayes Theorem; D012831:Bombyx; D004330:Drosophila; D029721:Drosophila Proteins; D019143:Evolution, Molecular; D005091:Exons; D020224:Expressed Sequence Tags; D006801:Humans; D007313:Insecta; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D012313:RNA / Q000378:metabolism; D034743:RNA-Induced Silencing Complex
D060565:Argonaute Proteins; D029721:Drosophila Proteins; D011506:Proteins; D034743:RNA-Induced Silencing Complex; C116498:piwi protein, Drosophila; D012313:RNA