XL43 and XL75: two novel RING finger-containing genes expressed during oogenesis and embryogenesis in Xenopus laevis.

This article reports on the isolation of two new Xenopus genes that encode two putative zinc finger proteins. The XL43 and XL75 proteins belong to the RBCC family, and also contains the rfp-like domain. XL43 and XL75 RNAs are found in the ovary, and myc-tagged proteins are detected in mRNA injected oocytes. Whole-mount in situ hybridization of embryos revealed that these two clones are expressed exclusively in neurectodermic and mesodermic tissues. The data suggest that XL43 and XL75 genes could play an important role in the frog's early development, perhaps as a transcription factor. This RBCC family, a subclass of the RING finger family, comprises proteins with known cellular transformation properties. All members possess, besides one RING finger motif, one or two B-boxes, each having a pair of zinc fingers, and a coiled coil domain (Borden, K.L. B. et al., 1996. Proc. Natl. Acad. Sci. USA 93, 1601-1606). Among this group, some members possess, besides the RING-B box-coiled coil (RBCC) motifs, a long C-terminal domain referred to as the rfp-like domain. Although its effective role has not been elucidated yet, this last domain could play an important role by binding a ligand (Bellini, M. et al., 1993. EMBO J. 12, 107-114).