RESUMO
ATHB17 (AT2G01430) is an Arabidopsis gene encoding a member of the α-subclass of the homeodomain leucine zipper class II (HD-Zip II) family of transcription factors. The ATHB17 monomer contains four domains common to all class II HD-Zip proteins: a putative repression domain adjacent to a homeodomain, leucine zipper, and carboxy terminal domain. However, it also possesses a unique N-terminus not present in other members of the family. In this study we demonstrate that the unique 73 amino acid N-terminus is involved in regulation of cellular localization of ATHB17. The ATHB17 protein is shown to function as a transcriptional repressor and an EAR-like motif is identified within the putative repression domain of ATHB17. Transformation of maize with an ATHB17 expression construct leads to the expression of ATHB17Δ113, a truncated protein lacking the first 113 amino acids which encodes a significant portion of the repression domain. Because ATHB17Δ113 lacks the repression domain, the protein cannot directly affect the transcription of its target genes. ATHB17Δ113 can homodimerize, form heterodimers with maize endogenous HD-Zip II proteins, and bind to target DNA sequences; thus, ATHB17Δ113 may interfere with HD-Zip II mediated transcriptional activity via a dominant negative mechanism. We provide evidence that maize HD-Zip II proteins function as transcriptional repressors and that ATHB17Δ113 relieves this HD-Zip II mediated transcriptional repression activity. Expression of ATHB17Δ113 in maize leads to increased ear size at silking and, therefore, may enhance sink potential. We hypothesize that this phenotype could be a result of modulation of endogenous HD-Zip II pathways in maize.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Deleção de Sequência/genética , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Zea mays/crescimento & desenvolvimento , Zea mays/genética , Transporte Ativo do Núcleo Celular , Motivos de Aminoácidos , Sequência de Aminoácidos , Proteínas de Arabidopsis/química , Peso Corporal/genética , Núcleo Celular/metabolismo , Sequência Consenso , Expressão Gênica , Dados de Sequência Molecular , Multimerização Proteica , Estrutura Quaternária de Proteína , Protoplastos/metabolismo , Reprodução , Fatores de Transcrição/química , Transcrição Gênica , Zea mays/citologia , Zea mays/fisiologiaRESUMO
Several human APOBEC3 deaminases can inhibit HIV-1 replication in vitro. HIV-1 Vif counteracts this restriction by targeting APOBEC3 for proteasomal degradation. Human APOBEC3H (A3H) is highly polymorphic, with natural variants differing considerably in anti-HIV-1 activity in vitro. To examine HIV-1 adaptation to variation in A3H activity in a natural infection context, we determined the A3H haplotypes and Vif sequences from 76 recently infected HIV-1 patients. We detected A3H-specific Vif changes suggesting viral adaptation. The patient-derived Vif sequences were used to engineer viruses that specifically differed in their ability to counteract A3H. Replication of these Vif-variant viruses in primary T cells naturally expressing active or inactive A3H haplotypes showed that endogenously expressed A3H restricts HIV-1 replication. Proviral DNA from A3H-restricted viruses showed high levels of G-to-A mutations in an A3H-specific GA dinucleotide context. Taken together, our data validate A3H expressed at endogenous levels as a bona fide HIV-1 restriction factor.
