A human gene previously identified as a partial cDNA homologous to the gene of RET finger protein was characterized. Northern hybridization detected three messages of 3.3, 4.2, and 7.5 kb. The coding sequences of the more abundant of the three messages, the 4.2 and the 3.3 kb, were determined. The former encodes a 630 amino acid protein (TRIM41alpha) and the latter a 518 amino acid protein (TRIM41beta). Green fluorescent protein (GFP) fusions of full-length TRIM41alpha and TRIM41beta were both observed as speckles in the cytoplasm and the nucleus. The result was corroborated by Western analysis of cellular fractions. Results with GFP fusions of various segments of the TRIM41 proteins indicated that the nuclear transport of the proteins is mediated by an N-terminal segment common to both isoforms, but independent of a classical nuclear localization signal sequence.