Bulky hydrophobic residues are interspersed throughout both terminal regions, reminiscent of many transcriptional activation domains ( 25– 27). The N terminus is enriched for acidic amino acids (20.5% Glu or Asp), whereas the C terminus is relatively proline-rich (11%). The protein can be divided into three general regions: the N terminus (residues 1–151), a basic-leucine zipper DNA-binding and dimerization domain (residues 152–220), and the C terminus (residues 221–371). The primary structure of human LZIP is shown schematically in Fig. Materials and Methods Plasmid Constructs. HCF-1 may thus act as a molecular chaperone, promoting the association of DNA-binding transcription factors with other transcriptional coactivators. Interestingly, mutation of the LxxLL motifs significantly reduces transactivation by LZIP without affecting the interaction with the HCF-1 β-propeller, suggesting that the LxxLL motifs interact with other regions of HCF-1 or recruit additional cellular factors required for activation. In temperature-shifted tsBN67 cells, loss of LZIP-mediated transactivation occurs within a few hours. Optimal transcriptional activation by LZIP requires direct interaction with HCF-1 and is observed by using a heterologous DNA-binding domain demonstrating that HCF-1 does not act by modulating the DNA-binding properties of LZIP. In this report, we show that the N terminus of LZIP (residues 1–92) contains a potent transcriptional activation domain composed of three functional elements: a pair of LxxLL motifs and the HBM. The functional relevance of the LZIP-HCF-1 interaction has yet to be determined. The LxxLL motifs are not required for association with the HCF-1 β-propeller and instead interact with other regions in HCF-1 or recruit additional cofactors. LZIP is an example of a sequence-specific DNA-binding protein that uses LxxLL motifs within its activation domain to stimulate transcription. LxxLL motifs are found in a number of transcriptional coactivators and mediate protein–protein interactions, notably recognition of the nuclear hormone receptors. Herein, we show that the N-terminal 92 amino acids of LZIP contain a potent transcriptional activation domain composed of three elements: the HCF-binding motif and two LxxLL motifs. Both LZIP and VP16 contain a four-amino acid HCF-binding motif, recognized by the N-terminal β-propeller domain of HCF-1. In addition to VP16, HCF-1 associates with a cellular bZIP protein known as LZIP (or Luman). HCF-1 is expressed in all cells and is required for progression through G 1 phase of the cell cycle. Association between HCF and VP16 leads to the assembly of a multiprotein enhancer complex that stimulates viral immediate-early gene transcription.
#Lzip multiple volume Activator
Host Cell Factor-1 (HCF-1, C1) was first identified as a cellular target for the herpes simplex virus transcriptional activator VP16.
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