RESUMEN
Human immunodeficiency virus type 1 (HIV-1) entry into target cells is a multistep process initiated by envelope protein gp120 binding to cell surface CD4. The conformational changes induced by this interaction likely favor a second-step interaction between gp120 and a coreceptor such as CXCR4 or CCR5. Here, we report a spontaneous and stable CD4-independent entry phenotype for the HIV-1 NDK isolate. This mutant strain, which emerged from a population of chronically infected CD4-positive CEM cells, can replicate in CD4-negative human cell lines. The presence of CXCR4 alone renders cells susceptible to infection by the mutant NDK, and infection can be blocked by the CXCR4 natural ligand SDF-1. Furthermore, we have correlated the CD4-independent phenotype with seven mutations in the C2 and C3 regions and the V3 loop. We propose that the mutant gp120 spontaneously acquires a conformation allowing it to interact directly with CXCR4. This virus provides us with a powerful tool to study directly gp120-CXCR4 interactions.
Asunto(s)
Genes env , VIH-1/genética , Mutación , Secuencia de Bases , Sitios de Unión/genética , Antígenos CD4/fisiología , Línea Celular , Quimera/genética , Clonación Molecular , Cartilla de ADN/genética , Proteína gp120 de Envoltorio del VIH/química , Proteína gp120 de Envoltorio del VIH/genética , Proteína gp120 de Envoltorio del VIH/fisiología , VIH-1/aislamiento & purificación , VIH-1/patogenicidad , Células HeLa , Humanos , Fenotipo , Receptores CXCR4/fisiologíaRESUMEN
A complementary deoxyribonucleic acid (cDNA) clone encoding an alpha thyroid hormone receptor (TR alpha) from muscovy duckling liver was isolated and sequenced. Comparison with the chicken TR alpha sequence showed a high degree of homology. Despite 45 nucleotide substitutions, the deduced peptide sequence was similar. This cDNA was used as a probe to characterize the TR alpha mRNA transcripts expressed in muscovy duckling liver and skeletal muscle.
Asunto(s)
Receptores de Hormona Tiroidea/biosíntesis , Transcripción Genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Northern Blotting , Pollos , Clonación Molecular/métodos , Cartilla de ADN , ADN Complementario , Patos , Hígado/metabolismo , Datos de Secuencia Molecular , Músculo Esquelético/metabolismo , Reacción en Cadena de la Polimerasa , ARN Mensajero/biosíntesis , Homología de Secuencia de AminoácidoRESUMEN
A cDNA clone encoding a beta-thyroid hormone receptor (TRbeta) from muscovy duckling liver was isolated and sequenced. Comparison with the chicken TRbeta sequence showed a high degree of homology. This cDNA was used as a probe to characterize the TRbeta mRNA transcripts expressed in muscovy duckling liver.