MOLECULAR ANALYSIS OF XENOPUS-LAEVIS SPARC (SECRETED PROTEIN, ACIDIC, RICH IN CYSTEINE) - A HIGHLY CONSERVED ACIDIC CALCIUM-BINDING EXTRACELLULAR-MATRIX PROTEIN

SPARC (Secreted Protein, Acidic, Rich in Cysteine) is expressed as a 1.6 kb mRNA in Xenopus laevis. On the basis of cDNA sequence analysis, Xenopus SPARC has a core M(r) of 32643, with one potential N-glycosylation site. Western analysis of SPARC isolated from Xenopus long bone indicates that the mature protein has an M(r) of 43 000. At the amino acid level, Xenopus SPARC has 78-79% sequence similarity to mouse, bovine and human SPARC. The least-conserved region is found within the N-terminal glutamic acid-rich domain, with the C-terminal Ca2+-binding domain being the most conserved. Adult Xenopus tissues show the same pattern of tissue-specific distribution of SPARC mRNAs as adult mouse.