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• _5 wasQuotedFrom 9774637 provenance.
• _5 value "The human HOXB1 gene codes for a 296-aa protein with 197 aa at the N terminus and 39 aa at the C terminus of the HD (1). We had previously reported (9) that the HOXB1 protein can cooperatively activate transcription, together with PBX1, from an autoregulatory element directing spatially restricted expression of the murine Hoxb-1 gene (b1-ARE) in the developing hindbrain (32). Selective recognition of the b1-ARE and transcriptional activation are mediated by HOXB1, while DNA-binding and protein-protein interaction functions of both HOXB1 and PBX1 are required for the assembly of a transcriptionally active complex (9). To localize the transcriptional activation domain of the complex, constructs coding for the full-length HOXB1 protein and three proteins with N-terminal deletions were cotransfected with the PBX1a expressor in the murine embryonal carcinoma cell line P19, together with a luciferase reporter construct (pAdMLARE) in which the 148-bp b1-ARE controls the adenovirus major late promoter. Deletion of the first 38 aa of HOXB1 (B1Delta 1-38) had no effect on the activity of the HOXB1-PBX1a complex, which was able to transactivate the pAdMLARE reporter 30- to 50-fold over the basal activity (Fig. 4B, column 7). Deletion of the first 90 aa (B1Delta 1-90) virtually abolished the activity of the complex (column 8), which showed a residual, eightfold activation level indistinguishable from that of the B1Delta 1-90 protein in the absence of PBX1 (column 4). An N-terminal deletion up to aa 155, which does not affect the FDWM domain necessary for cooperative interaction with PBX1 (9), further reduced the activity of the complex, down to three times the reporter basal activity (column 9). All HOXB1 mutants bound cooperatively to the R3 core element (TGATGGATGAG) of the b1-ARE together with PBX1, as checked by EMSA with in vitro-translated proteins (reference 9 and data not shown). These data indicate that the transcriptional activation domain of the HOXB1 protein in the context of the HOXB1-PBX1a complex resides between aa 38 and 90, a Ser-Pro-rich (20%) region only slightly conserved in the N termini of other vertebrate group 1 Hox genes (Fig. 5). The N-terminal region from aa 38 to 90 also contains most of the activating functions when tested in the presence of Prep1, a recently identified PBX1 cofactor forming a HOXB1-PBX1-Prep1 ternary complex on the b1-ARE (5)." provenance.