Modification of human beta-globin locus PAC clones by homologous recombination in Escherichia coli.

We report here modifications of human beta-globin PAC clones by homologous recombination in Escherichia coli DH10B, utilising a plasmid temperature sensitive for replication, the recA gene and a wild-type copy of the rpsL gene which allows for an efficient selection for plasmid loss in this host. High frequencies of recombination are observed even with very small lengths of homology and the method has general utility for introducing insertions, deletions and point mutations. No rearrangements were detected with the exception of one highly repetitive genomic sequence when either the E.COLI: RecA- or the lambdoid phage encoded RecT and RecE-dependent recombination systems were used.

Alternative translation initiation site usage results in two functionally distinct forms of the GATA-1 transcription factor.

GATA-1 is a zinc-finger transcription factor that plays a critical role in the normal development of hematopoietic cell lineages. In human and murine erythroid cells a previously undescribed 40-kDa protein is detected with GATA-1-specific antibodies. We show that the 40-kDa GATA-1 (GATA-1s) is produced by the use of an internal AUG initiation codon in the GATA-1 transcript. The GATA-1 proteins share identical binding activity and form heterodimers in erythroleukemic cells but differ in their transactivation potential and in their expression in developing mouse embryos.

CTF/NF-1 binds the stage selector element of the human gamma-globin gene promoter.

The human gamma-globin gene undergoes to a transcriptional switch during development, being expressed in the fetus and silenced at birth. It has been proposed that the sequence centered at -50 of the gamma-globin promoter contains a stage selector element (SSE) involved in the gamma- to beta-globin switching. The presence of the SSE confers preferential functional interactions of the promoter with the locus control region (LCR) in the fetal liver. It has been shown that two factors bind the gamma-globin SSE: Sp1 and the stage selector protein (SSP). Here we show that also the ubiquitous transcription factor CTF/NF-1 binds to the -53 to -35 element of the human gamma-globin promoter and its specificity is not influenced by flanking sequences.

Differential binding of the NFE3 and CP1/NFY transcription factors to the human gamma- and epsilon-globin CCAAT boxes.

Naturally occurring nondeletional mutations affecting the distal CCAAT box of the human gamma-globin gene promoter result in hereditary persistence of fetal hemoglobin in adult life. Although the distal CCAAT box is the target of several factors, including CP1/NFY, CDP, GATA-1 and NFE3, only NFE3 binding activity is consistently sensitive to well characterized mutations in this region such as G-117-->A, C-114-->T, and delta 13 hereditary persistence of fetal hemoglobin. We extensively characterized the binding specificities of NFE3 and demonstrated that NFE3 has unique properties with respect to other CCAAT box-binding proteins. Affinity-purified NFE3 from erythroid K562 cells binds the distal but not the proximal human gamma-globin CCAAT box, the single CCAAT box of the human epsilon-globin promoter, and the proximal CCAAT box of the evolutionarily related Galago crassicaudatus gamma-globin gene. Within the epsilon-globin CCAAT box, NFE3 represents the major and almost exclusive binding activity. Disruption of such a binding site essentially inactivates the epsilon-globin promoter, suggesting that NFE3 plays an important role in the embryonic expression of this gene.

Overexpression and amplification of the met/HGF receptor gene during the progression of colorectal cancer.

The c-met oncogene encodes the receptor for hepatocyte growth factor/scatter factor, a potent mitogen for epithelial cells that also promotes cell motility and invasiveness. We have studied the changes of c-met gene expression that occur during the progression of colorectal tumors. Sixteen adenomas, 123 primitive carcinomas, and 25 liver metastases were examined. In several instances it was possible to compare same-patient samples of normal colon mucosa against primary tumor and primary carcinoma against synchronous metastasis. The expression of the c-met gene was increased from 5- to 50-fold in about 50% of tumors, at any stage of progression, and in 70% of liver metastases. Overexpression was associated with amplification of the c-met gene in only 10% of carcinomas, but in 8 of 9 metastases examined. These data suggest that overexpression of the c-met oncogene contributes a selective growth advantage to neoplastic colorectal cells at any stage of tumor progression. Moreover, amplification appears to give a further selective advantage for the acquisition of metastatic potential.

Expression, purification, and functional characterization of the two zinc-finger domain of the human GATA-1.

The DNA-binding domain of the erythroid transcription factor GATA-1 consists of two closely related, but distinct zinc-fingers which are highly conserved among the members of the growing family of GATA-like factors. The DNA-binding domain of the human GATA-1 (F1F2) was expressed as a histidine-tagged fusion protein in Escherichia coli. The denaturated protein was purified by Ni(2+)-chelate affinity chromatography and renaturated in situ. The active recombinant protein was purified by DNA affinity chromatography. F1F2 displayed GATA-1 specific binding activity toward its DNA recognition sequences within the hypersensitive site 3 of the human locus control region and the human gamma-globin promoter. In contrast to GATA-1 protein purified from K562 nuclei, the recombinant F1F2 bound also the CCAAT-box region of the human gamma-globin promoter.