Identification and characterization of Psx-2, a novel member of the Psx (placenta-specific homeobox) family

Psx (now designated as Psx-1) is a murine placenta-specific homeobox gene. Here, we report the isolation and characterization of a second mouse Psx ge ne (Psx-2). Although 29 bp were absent towards the 3' end of Psx-2, Psx-2 a nd Psx-1 cDNA had identical 5' and 3' ends. Overall sequence identity betwe en the two cDNAs was 91 % at the nucleotide level and 81 % at the amino aci d level. Both Psx proteins contain 227 amino acids. These results suggest t hat they arose through a recent gene duplication. A surprising finding is t hat the 81 % sequence identity between Psx-1 and Psx-2 proteins drops at th e level of homeodomain to 78 %. Further, the amino acid at position 51, whi ch is invariably an asparagine in other homeodomains and is known to contac t DNA directly, is a methionine in the homeodomains of both Psx-1 and Psx-2 . This suggests that Psx proteins may inter-act with DNA sequences differen tly to those bound by other homeodomains. Southern blot analysis indicated that the two Psx genes occur on separate loci in the mouse genome. The Psx- 2 gene spans approx. 2.6 kb of mouse genome, and contains four exons and th ree introns. (C) 2000 Elsevier Science B.V. All rights reserved.