Differential utilization of the same reading frame in a Xenopus homeobox gene encodes two related proteins sharing the same DNA-binding specificity.

Abstract

Xenopus XlHbox 1 produces two transcripts during early development. One encodes a long open reading frame (ORF) and the other a short ORF sharing the same homeodomain, but differing by an 82 amino acid domain at the amino terminus. The long protein amino terminus is conserved with many other homeodomain proteins, and its absence from the short protein could have functional consequences. Some viral genes also utilize a single ORF to encode transcription factors of antagonistic functions. The overall organization of the homologous genes in frog and man is similar, supporting the notion that both transcripts are of functional significance. Studies on XlHbox 1 function show that the region common to the long and short proteins has a sequence‐specific DNA‐binding activity, and that microinjection of specific antibodies into embryos results in the loss of structures derived from cells normally expressing XlHbox 1.

Characterization of the Xenopus Hox 2.4 gene and identification of control elements in its intron

“…When the 154 bp fragment was subjected to DNAse I footprint analysis, at least two regions (F1 and F2, Fig. 2) were protected (Cho et al, 1988). The core sequences of these footprints resemble the Drosophila Antennapedia and engrailed homeobox binding consensus sequence CAATTAAA.…”

“…A 154 bp Sau3A fragment identified by DNA immunoprecipitation is boxed with a solid line, and is located at position 51 1 to 664. F1 and F2 indicate nucleotide sequences previously identified by Anfennapedia-type homeobox binding studies (Cho et al, 1988) and are overlined. The Sac I sites from which both the RNA probe (pS400) and the fusion protein for the antibody were constructed are boxed at positions 44 and 410.…”

“…We had shown by DNAse I footprinting assay that a Hox 3.3 (XIHbox 1) fusion protein can bind to a sequence (CAATTAAA) recognized by a number of homeodomain proteins in vitro (Cho et al, 1988). For that study, we used the Hox 2.3 promoter region (2.2 kb Hind111 fragment; see Figs.…”

“…Briefly, a plasmid containing the Hox 2.3 promoter was digested with Sau 3A, radiolabeled, and allowed to form proteidDNA complexes with the Hox 3.3 fusion protein (Desplan et al, 1985;Benson and Pirrotta, 1987). The complexes were then immunoprecipitated using protein A Sepharose beads bound with anti-P-galactosidase antibody, washed, and eluted (Cho et al, 1988). We were able to enrich a 154 bp Sau 3A fragment that specifically bound to the laze-homeodomain fusion protein.…”

“…The boundaries of the 154 bp fragment containing the homeodomain binding sites are marked by the two arrows. F1 and F2, the previously identified footprints (Cho et al, 1988), are overlined. (Laimins et al, 1984), as shown in the diagram.…”