Induction of HoxB transcription by retinoic acid requires actin polymerization

We have analyzed the role of actin polymerization in retinoic acid (RA)-induced HoxB transcription, which is mediated by the HoxB regulator Prep1. RA induction of the HoxB genes can be prevented by the inhibition of actin polymerization. Importantly, inhibition of actin polymerization specifically affects the transcription of inducible Hox genes, but not that of their transcriptional regulators, the RARs, nor of constitutively expressed, nor of actively transcribed Hox genes. RA treatment induces the recruitment to the HoxB2 gene enhancer of a complex composed of "elongating" RNAPII, Prep1, beta-actin, and N-WASP as well as the accessory splicing components p54Nrb and PSF. We show that inhibition of actin polymerization prevents such recruitment. We conclude that inducible Hox genes are selectively sensitive to the inhibition of actin polymerization and that actin polymerization is required for the assembly of a transcription complex on the regulatory region of the Hox genes.

The complete nucleotide sequence of a Spanish isolate of Citrus psorosis virus: comparative analysis with other ophioviruses

The complete genomic sequence (11278 nt) of Citrus psorosis virus (CPsV), isolate P-121 from Spain, was determined and compared with those from isolate CPV-4 and from other ophioviruses. The three RNAs of P-121 had similar size and identical organization as those of CPV-4. The 24K and the RdRp proteins were potentially encoded in the viral complementary (vc) strand of RNA 1, the 54K protein potentially encoded in vcRNA 2 and the coat protein encoded in vcRNA 3. These four proteins from P-121 and CPV-4 had 87, 92, 93 and 94% amino acid identity, respectively, but only 22, 38, 25 and 33% identity with their homologous proteins from Mirafiori lettuce big vein virus (MLBVV), the only other ophiovirus completely sequenced. Biological and genetic differences between CPsV and MLBVV (and the other ophioviruses), would support their future allocation in different genera within a tentative family Ophioviridae.

Citrus psorosis virus RNA 1 is of negative polarity and potentially encodes in its complementary strand a 24K protein of unknown function and 280K putative RNA dependent RNA polymerase

Citrus psorosis virus (CPsV), the type member of genus Ophiovirus, has three genomic RNAs. Complete sequencing of CPsV RNA 1 revealed a size of 8184 nucleotides and Northern blot hybridization with chain specific probes showed that its non-coding strand is preferentially encapsidated. The complementary strand of RNA 1 contains two open reading frames (ORFs) separated by a 109-nt intergenic region, one located near the 5'-end potentially encoding a 24K protein of unknown function, and another of 280K containing the core polymerase motifs characteristic of viral RNA-dependent RNA polymerases (RdRp). Comparison of the core RdRp motifs of negative-stranded RNA viruses, supports grouping CPsV, Ranunculus white mottle virus (RWMV) and Mirafiori lettuce virus (MiLV) within the same genus (Ophiovirus), constituting a monophyletic group separated from all other negative-stranded RNA viruses. Furthermore, RNAs 1 of MiLV, CPsV and RWMV are similar in size and those of MiLV and CPsV also in genomic organization and sequence.