"To ask whether this redundancy resulted from a functional equivalence between the two factors, we performed a series of experiments in which forced expression of one Hox family member was carried out in a genetic background lacking endogenous
lin-39 and
mab-5 activity. Rescue was assayed by direct analysis of differentiated descendants of the M lineage using specific integrated reporter constructs (Fig. 1; see Materials and Methods for details of reporter constructs used). We found that expression of either MAB-5 or LIN-39 from a heat shock promoter using a periodic heat shock regimen to maintain levels of MAB-5 or LIN-39 was sufficient for full or partial rescue of the M lineage defects (Fig. 3). Expression of either coding region from a 7 kb segment of the
mab-5 promoter also gave rescue (although rescue was somewhat less effective in this case; Fig. 3)."