Mouse serum amyloid P-component (SAP) levels controlled by a locus on chromosome 1

Systems genetics of the lateral septal nucleus in mouse: heritability, genetic control, and covariation with behavioral and morphological traits

The lateral septum has strong efferent projections to hypothalamic and midbrain regions, and has been associated with modulation of social behavior, anxiety, fear conditioning, memory-related behaviors, and the mesolimbic reward pathways. Understanding natural variation of lateral septal anatomy and function, as well as its genetic modulation, may provide important insights into individual differences in these evolutionarily important functions. Here we address these issues by using efficient and unbiased stereological probes to estimate the volume of the lateral septum in the BXD line of recombinant inbred mice. Lateral septum volume is a highly variable trait, with a 2.5-fold difference among animals. We find that this trait covaries with a number of behavioral and physiological phenotypes, many of which have already been associated with behaviors modulated by the lateral septum, such as spatial learning, anxiety, and reward-seeking. Heritability of lateral septal volume is moderate (h(2) = 0.52), and much of the heritable variation is caused by a locus on the distal portion of chromosome (Chr) 1. Composite interval analysis identified a secondary interval on Chr 2 that works additively with the Chr 1 locus to increase lateral septum volume. Using bioinformatic resources, we identified plausible candidate genes in both intervals that may influence the volume of this key nucleus, as well as associated behaviors.

Characterization of Bglu3, a mouse fasting glucose locus, and identification of Apcs as an underlying candidate gene

Bglu3 is a quantitative trait locus for fasting glucose on distal chromosome 1 identified in an intercross between C57BL/6 (B6) and C3H/HeJ (C3H) apolipoprotein E-deficient (apoE(-/-)) mice. This locus was subsequently replicated in two separate mouse intercrosses. The objective of this study was to characterize Bglu3 through construction and analysis of a congenic strain and identify underlying candidate genes. Congenic mice were constructed by introgressing a genomic region harboring Bglu3 from C3H.apoE(-/-) into B6.apoE(-/-) mice. Mice were started with a Western diet at 6 wk of age and maintained on the diet for 12 wk. Gene expression in the liver was analyzed by microarrays. Congenic mice had significantly higher fasting glucose levels and developed more significant glucose intolerance compared with B6.apoE(-/-) mice on the Western diet. Microarray analysis revealed 336 genes to be differentially expressed in the liver of congenic mice. Further pathway analysis suggested a role for acute phase response signaling in regulating glucose intolerance. Apcs, encoding an acute phase response protein serum amyloid P (SAP), is located underneath the linkage peak of Bglu3. Multiple single nucleotide polymorphisms between B6 and C3H mice were detected within and surrounding Apcs. Apcs expression in the liver was significantly higher in congenic and C3H mice compared with B6 mice. The Western diet consumption led to a gradual rise in plasma SAP levels, which was accompanied by rising fasting glucose in both B6 and C3H apoE(-/-) mice. Expression of C3H Apcs in B6.apoE(-/-) mice aggravated glucose intolerance. Bglu3 is confirmed to be a locus affecting diabetes susceptibility, and Apcs is a probable candidate gene.

Genetic linkage of hyperglycemia, body weight and serum amyloid-P in an intercross between C57BL/6 and C3H apolipoprotein E-deficient mice

Dyslipidemia and hyperglycemia are integral components of the metabolic perturbations in type 2 diabetes. Apolipoprotein E-deficient (apoE(-/-)) mice develop severe hyperlipidemia and significant hyperglycemia when fed a western diet containing 21% fat (w/w), 0.15% cholesterol and 19.5% casein. Using an intercross between C57BL/6J (B6) and C3H/HeJ (C3H) apoE(-/-) mice, we performed quantitative trait locus (QTL) analysis to identify loci contributing to hyperglycemia and associated traits. Fasting plasma levels of glucose, insulin and serum amyloid-P (SAP) and body weight in 234 female F2 mice were measured after being fed the western diet for 12 weeks. QTL analysis revealed one significant QTL, named Bglu3 [95.8 cM, logarithm of odds ratio (OR)(LOD) 4.1], on chromosome 1 and a suggestive QTL on chromosome 9 (38 cM, LOD 2.3) that influenced plasma glucose levels. Bglu3 coincided with loci on distal chromosomal 1 that had a major influence on plasma SAP levels and body weight. Significant correlations between plasma glucose, SAP and body weight were observed in F2 mice. Thus, these results demonstrate genetic linkages of hyperglycemia and body weight with SAP, a marker of the acute-phase response, in hyperlipidemic apoE(-/-) mice and suggest a probability for the Sap gene to be a positional candidate of Bglu3.

Altered phenotype of dextran sulfate sodium colitis in interferon regulatory factor-1 knock-out mice

BACKGROUND AND AIMS

Interferon regulatory factor-1 (IRF-1) is a transcription factor with antiviral, proinflammatory and tumor suppressor properties. We examined the role of IRF-1 in dextran sulfate sodium colitis, a murine model of inflammatory bowel disease, to determine if absence of the gene would protect against colitis.

METHODS

C57BL/6J mice with a targeted disruption of IRF-1 and wild-type C57BL/6J controls received five 7-day cycles of 2% dextran sulfate sodium alternating with five 7-day cycles of water. Colonic tissue was formalin fixed for histological analysis and total RNA extracted for gene chip and SYBR green real-time polymerase chain reaction (PCR) analysis.

RESULTS

Histological analysis revealed increased distortion of crypt architecture in the dextran sulfate sodium-treated, IRF-1 -/- animals as compared to dextran sulfate sodium-treated wild-type animals. Five of 15 dextran sulfate sodium-treated IRF-1 -/- mice, but only one of 14 dextran sulfate sodium-treated wild-type mice, developed colonic dysplasia. Microarray analysis comparing colonic gene expression in IRF-1 -/- and wild-type animals revealed decreased expression of caspases, genes involved in antigen presentation, and tumor suppressor genes in the IRF-1 -/- animals. Increased expression of genes involved in carcinogenesis and immunoglobulin and complement genes was also noted in the knock-out animals.

CONCLUSIONS

Absence of IRF-1 is not protective in dextran sulfate sodium colitis.

Role of STAT3 and C/EBP in cytokine-dependent expression of the mouse serum amyloid P-component (SAP) and C-reactive protein (CRP) genes

Inflammation is accompanied by a rapid increase in blood levels of acute phase proteins synthesized by hepatocytes in response to cytokines. Although C-reactive protein (CRP) levels increase dramatically in most mammals, the major acute phase protein in the mouse is the homologous pentraxin, serum amyloid P-component (SAP), whereas CRP is a minor acute phase reactant. The molecular basis for the pronounced difference in SAP and CRP gene expression in the mouse is unknown. Transfection of ++/Li mouse hepatoma cells with CAT-reporter constructs containing the 5'-flanking region of the mouse CRP gene indicated that transcription was stimulated by either IL-6, or IL-6 plus IL-1, when > or =360 bp of the 5'-proximal DNA was present. Examination of the 5'-flanking region of the mouse SAP gene revealed that the region between -433 and -397 from the transcription start site responded to IL-1 and IL-6 by binding both STAT3 and C/EBPbeta. This responsive region consisted of two adjacent C/EBPbeta consensus sites that overlap with two STAT3 consensus sites and was found to bind C/EBPbeta at an upstream site of -427 to -409 and STAT3 at a downstream site of -415 to -397. By contrast, the 360 bp promoter of the CRP gene was bound only by STAT3 at consensus sites at -93, -142, -173, and -287 from the start site; however, a single consensus site for C/EBP at -75 was not recognized. STAT3 appears to be necessary for both mouse SAP and CRP gene transcription since overexpression of an inactive, deletion mutant of STAT3 inhibited transcription of both genes. The results indicate that both STAT3 and C/EBPbeta participate in mouse SAP gene expression, whereas only STAT3 is involved in mouse CRP gene expression. The findings for mouse SAP gene expression are consistent with the reported interaction between these two transcription factors for human CRP gene transcription.

Genetic control of the frequency of hematopoietic stem cells in mice: mapping of a candidate locus to chromosome 1

The genetic elements that govern the differentiation and proliferation of hematopoietic stem cells remain to be defined. We describe here marked strain-specific differences in the frequency of long-term culture-initiating cells (LTC-IC) in the bone marrow of different strains of mice. Mice of C57Bl/6 background showed the lowest levels of stem cells in marrow, averaging 2.4 +/- .06 LTC-IC/10(5) cells, BALB/c is intermediate (9.1 +/- 4.2/10(5) cells), and DBA/2 mice contained a 11-fold higher frequency of LTC-IC (28.1 +/- 16.5/10(5) cells) than C57Bl/6 mice. The genetic factors affecting the size of the stem cell pool were analyzed in the C57Bl/6 X DBA/2 recombinant inbred strains; LTC-IC frequencies ranged widely, indicating that stem cell frequencies are controlled by multiple genes. Quantitative trait linkage analysis suggested that two loci that have major quantitative effects are located on chromosome 1 near Adprp and Acrg, respectively. The mapping of the locus near Adprp was confirmed by finding an elevated stem cell frequency in B6.C-H25, a C57Bl/6 congenic strain that carries a portion of chromosome 1 derived from BALB/c mice. We have named this gene Scfr1 (stem cell frequency regulator 1). The allelic forms of this gene may be an important predictor of stem cell number and thus would be useful for evaluating cell sources in clinical stem cell transplantation.

Chromosome mapping of Rmp-4, a gonad-dependent gene encoding host resistance to mousepox

DBA/2 (D2) mice are susceptible and C57BL/6 (B6) mice are resistant to lethal mousepox. A congenic resistant strain, D2.B6-Rmp-4r (D2.R4), was developed by serially backcrossing male mice that survived ectromelia virus infection with D2 mice, beginning with (B6 x D2)F1 mice. Male D2.R4 mice were at least 300-fold more resistant to lethal mousepox than male D2 mice. Female D2.R4 mice were 100-fold more resistant than male D2.R4 mice and 500-fold more resistant than female D2 mice. Neonatal gonadectomy prevented development of resistance in D2.R4 mice of both sexes. Differences in resistance between strains and between sexes correlated with restriction of virus replication in spleen and liver, but gender differences were less evident in liver than in spleen. High-resolution interval mapping of the 19 autosomes of D2.R4 mice using dispersed informative microsatellites as marker loci revealed a segment of distal chromosome 1 to be of B6 origin. Haplotypes for a marker locus, D1Mit57, from the differential segment were determined in (D2.R4 x D2)F1 x D2 backcross mice, which were then infected with ectromelia virus. Significantly more heterozygotes than homozygotes survived ectromelia virus infection in both sexes. Whereas nearly all surviving males were heterozygotes, 44% of surviving females were homozygotes. These results indicate that resistance in D2.R4 mice is determined by a gonad-dependent gene on distal chromosome 1, provisionally named Rmp-4, and by an ovary-dependent factor that is not genetically linked to Rmp-4.

Regulation of mouse serum amyloid P gene expression by cytokines in vitro

Inflammation is accompanied by an increase in the plasma levels of a number of proteins collectively known as acute-phase reactants (APRs). Serum amyloid P component (SAP) is a major mouse APR: hepatic SAP mRNA and plasma SAP protein concentrations increase by up to 20-fold in mice undergoing an inflammatory response. In-vitro studies, using primary hepatocyte cultures, have previously shown that SAP mRNA and protein levels increase in response to stimulation with a variety of cytokines such as monocyte-conditioned medium (MCM), interleukin 1 (IL-1), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta). In this report, we have examined a mouse hepatoma cell line in which SAP gene regulation closely resembles that of primary hepatocytes. Accumulation of SAP mRNA in the +/+ Li mouse hepatoma cell line after stimulation with MCM, IL-1, IL-6 and the combination of IL-1 and IL-6 was demonstrated. This increase in the cellular content of SAP mRNA did not require new protein synthesis and was at least partially due to an increase in the transcription rate of the SAP gene.

The strain-dependent constitutive expression of murine serum amyloid-P component is regulated at the transcriptional level

The strain-dependent expression of murine serum amyloid P-component (SAP) has been known to be linked to the Sap locus. We have quantified the SAP mRNA in several inbred strains including DBA/2 and C57BL/6 mice which represent high and low producers of SAP at resting state, respectively, and found that the mRNA levels correlated well with the amount of SAP protein. Interestingly, the SAP mRNA level of F1 mouse between DBA/2 and C57BL/6 was low and similar to that of C57BL/6. Primer extension and ribonuclease (RNAase) protection analyses demonstrated that a single type of transcript was generated from the SAP gene and that the cap sites were identical regardless mouse strains tested under unstimulated and stimulated (by lipopolysaccharide (LPS) or interleukin-6 (IL-6)) conditions. To investigate possible structural difference of the SAP gene including 5' flanking region, we have cloned, sequenced and compared the SAP genes from DBA/2 and C57BL/6 mice. Sequence analyses revealed that the 5' flanking regulatory regions, as well as the coding regions, were well-conserved between the two strains. These results demonstrate that the strain-dependent SAP expression occurs at the transcriptional level but seems to be affected by neither different type of the transcripts nor structural difference of the 5' flanking and coding regions of the SAP gene. It was suggested that a possible transcription factor with suppressive activity, which is encoded by a gene linked to Sap, may be involved.

Mouse C-reactive protein. Generation of cDNA clones, structural analysis, and induction of mRNA during inflammation

A full-length C-reactive protein (CRP) cDNA clone has been isolated from a CBA/J-strain-mouse acute-phase liver library. The 1614-nucleotide cDNA specifies mRNA 5' and 3' untranslated regions of 81 and 858 bases respectively that flank 675 bases encoding mouse pre-CRP. The derived amino acid sequence predicts a 19-residue leader peptide followed by a 206-residue mature mouse CRP that shows considerable sequence identity with both human and rabbit CRP. Northern-blot analysis of mouse liver CRP mRNA concentrations after inflammatory stimuli and comparison with hepatic induction of mRNA for the major mouse acute-phase protein serum amyloid P component established that CRP, a major acute-phase reactant in human and rabbit, is a minor acute-phase reactant in mouse. The size and organization of the mouse CRP mRNA 5' and 3' untranslated regions are significantly different from those of human and rabbit CRP mRNA and may have implications for its anomalous minimal induction during acute inflammation.

Characterization of the gene encoding mouse serum amyloid P component. Comparison with genes encoding other pentraxins

A CBA/J-strain mouse serum amyloid P component (SAP) genomic clone was isolated and analysed. The clone contains the entire SAP gene and specifies a primary transcript of 1065 nucleotide residues. This comprises a first exon of 206 nucleotide residues containing the mRNA 5'-untranslated region and sequence encoding the pre-SAP leader peptide and the first two amino acid residues of mature SAP separated by a single 110-base intron from a 749-nucleotide-residue second exon containing sequence encoding the bulk of the mature SAP and specifying the mRNA 3'-untranslated region. The overall organization is similar to that of the human SAP gene, and the coding region and intron sequences are highly conserved. The SAP RNA cap site was defined by primer extension analysis of polyadenylated acute-phase liver RNA. The 5'-region of the mouse SAP gene contains modified CAAT and TATA promoter elements preceded by a putative hepatocyte-nuclear-factor-1-recognition site; these structures are in a region that is highly homologous to the corresponding region of the human SAP gene. Comparisons of the mouse SAP gene structure and derived amino acid sequence with those of other mammalian pentraxins were made.

Physical mapping of a family of interferon-activated genes, serum amyloid P-component, and alpha-spectrin on mouse chromosome 1

This report defines genetic and physical relationships among alpha-spectrin (Spna-1), serum amyloid P-component (Sap), and a family of interferon-activated genes, provisionally designated Ifi202, Ifi203, and Ifi204. By linkage analysis using a large panel of interspecific backcross mice, Sap, Ifi202, and Ifi204 were shown to be tightly linked to Spna-1 on distal mouse chromosome 1. By pulsed field electrophoresis, a genomic restriction map of 6400 kb of distal mouse chromosome 1 was generated, linking genes encoding Sap, (Ifi202, Ifi203, Ifi204), and Spna-1 in that order within 450-1000 kb (where the genes within brackets were not ordered). The interferon-activated genes Ifi202, Ifi203, and Ifi204 were linked within 75-150 kb. Furthermore, genes transcriptionally activated by cytokines, namely Sap, Ifi202, Ifi203, and Ifi204, were located within 450 kb. These studies suggest the possibility that selective pressure may maintain in physical proximity gene clusters which are under coordinate transcriptional control.

Interferons as gene activators: a cluster of six interferon-activatable genes is linked to the erythroid alpha-spectrin locus on murine chromosome 1

Several interferon-activatable murine genes were mapped to murine chromosomes by hybridizing cDNA probes to Southern blots of genomic DNA samples from a panel of mouse-hamster somatic cell hybrid lines. The 12 gene is located on chromosome 12 and it specifies a 3.6-kb mRNA. The 204 gene (specifying a 2.5-kb mRNA), and three genes of the 203 gene family (hybridizing to five mRNAs of sizes between 2 and 4.5 kb), together with the 202 gene (specifying a 2-kb mRNA) are located on murine chromosome 1. By restriction fragment length polymorphism analysis of DNA samples prepared from a panel of recombinant inbred mouse lines (C57BL/6J D DBA/2J) and from 85 [C3H/HeJ-gld/gld x Mus spretus) F1 X C3H/HeJ-gld/gld] backcross mice we established a close linkage of the 202, 203, and 204 genes to the erythroid alpha-spectrin gene (Spna-1) on distal murine chromosome 1. Cosmids containing the 202, 203, and 204 genes were isolated from a library derived from AKR mouse DNA. Southern blot analysis of such cosmids revealed: (a) hybridization of a partial 203 cDNA to three genes of the 203 gene family; (b) cross-hybridization of the 202 and 204 genes with one another and with a third gene (designated as 201 gene), and (c) a close linkage of genes of the 203 family with the 201, 202, and 204 genes. These results indicate the existence of a cluster of at least six closely linked, interferon-activatable genes on distal murine chromosome 1 in the vicinity of the Spna-1 locus and also of the Minor lymphocyte stimulating locus (Mlsa).

Chromosomal location of the gene encoding the murine acute-phase protein serum amyloid P-component (SAP)

A full-length cDNA clone, pmSAP3, encoding, the serum P component (SAP), has been used to search for DNA fragment length variation among mouse strains previously analyzed for differences in endogenous SAP levels. Three alleles were found using EcoRI-digested DNA. The finding of a single 5.4-kb fragment, allele d, in DNA from DBA/2J mice suggests the presence of a single Sap locus. Segregation of DNA fragment associated with Sapb and Sapd alleles was analyzed in three sets of recombinant inbred (RI) strains. The strain distribution pattern found for the Sap alleles was identical to that of alleles of Ly-9 in 43 individual RI strains, suggesting tight linkage with Ly-9 on mouse chromosome 1. In the BXD RI strains, the SDP of the Sap locus, defined by the difference in the endogenous SAP level, is also identical to the SDP of the DNA fragments. We propose to redesignate the Sap locus to include both the structural element defined by the DNA polymorphism and the regulatory element involved in the regulation of SAP synthesis. The Sap locus is the major genetic element contributing to the regulation of SAP production. Other genetic factors are also involved, as shown by the presence of nonparental phenotypes in the individual BXH RI strains.

Genetic relationships of Mlsa among polymorphic loci on distal mouse chromosome 1

The segregation of Mlsa with respect to genes localized distally on mouse chromosome 1 was examined in two sets of recombinant inbred (RI) strains. In order to localize Mlsa, a linkage map based on analysis of both interspecific backcross mice and multiple sets of RI strains was utilized: (centromere) - Ren-1,2 - 10 centimorgans (cM) - At-3 - 8cM-Apo-A2/Ly-17 - 2cM - Spna-1 - 4cM - Akp-1 - (telomere). The Mlsa allele was mapped to a region that extended just centromeric of Ly-17 (one crossover in 40 RI strains) to just telomeric of Spna-1 (no crossover in 40 RI strains). The identification of multiple polymorphic loci in the region of Mlsa should allow precise gene localization and assist in efforts to clone this gene.

Chromosomal localization of human Na+, K+-ATPase alpha- and beta-subunit genes

Na+, K+-ATPase is a heterodimeric enzyme responsible for the active maintenance of sodium and potassium gradients across the plasma membrane. Recently, cDNAs for several tissue-specific isoforms of the larger catalytic alpha-subunit and the smaller beta-subunit have been cloned. We have hybridized rat brain and human kidney cDNA probes, as well as human genomic isoform-specific DNA fragments, to Southern filters containing panels of rodent X human somatic cell hybrid lines. The results obtained have allowed us to assign the loci for the ubiquitously expressed alpha-chain (ATP1A1) to human chromosome 1, region 1p21----cen, and for the alpha 2 isoform that predominates in neural and muscle tissues (ATP1A2) to chromosome 1, region cen----q32. A common PstI RFLP was detected with the ATP1A2 probe. The alpha 3 gene, which is expressed primarily in neural tissues (ATP1A3), was assigned to human chromosome 19. A fourth alpha gene of unknown function (alpha D) that was isolated by molecular cloning (ATP1AL1) was mapped to chromosome 13. Although evidence to date had suggested a single gene for the beta-subunit, we found hybridizing restriction fragments derived from two different human chromosomes. On the basis of knowledge of conserved linkage groups on human and murine chromosomes, we propose that the coding gene ATP 1B is located on the long arm of human chromosome 1 and that the sequence on human chromosome 4 (ATP 1BL1) is either a related gene or a pseudogene.

Establishment of a molecular genetic map of distal mouse chromosome 1: further definition of a conserved linkage group syntenic with human chromosome 1q

A linkage map of distal mouse chromosome 1 was constructed by restriction fragment length polymorphism analysis of DNAs from seven sets of recombinant inbred (RI) strains. The data obtained with seven probes on Southern hybridization combined with data from previous studies suggest the gene order Cfh, Pep-3/Ren-1,2, Ly-5, Lamb-2, At-3, Apoa-2/Ly-17,Spna-1. These results confirm and extend analyses of a large linkage group which includes genes present on a 20-30 cM span of mouse chromosome 1 and those localized to human chromosome 1q21-32. Moreover, the data indicate similar relative positions of human and mouse complement receptor-related genes REN, CD45, LAMB2, AT3, APOA2, and SPTA. These results suggest that mouse gene analyses may help in detailed mapping of human genes within such a syntenic group.

Chromosome maps of man and mouse, III

Data on loci whose positions are known in both man and mouse are presented in the form of chromosomal displays, a table, and autosomal and X-chromosomal grids. At least 40 conserved autosomal segments with two or more loci, as well as 17 homologous X-linked loci, are now known in the two species, in which mitochondrial DNA is also highly conserved. Apart from the Y, the only chromosome now lacking a conserved group is human 13. Human 17 has a single conserved group which includes both short and long arms, and so may have remained largely intact in mammalian evolution. Human and mouse chromosomal maps show the approximate locations of homologous genes while the mouse map also shows the positions of translocations used in gene location.

Regulation of the antibody response by the acute phase reactant: mouse serum amyloid P-component (SAP)

Serum amyloid P-component (SAP) is the major acute phase reactant (APR) of mice. Purified mouse SAP at 0.1 to 10.0 micrograms/ml selectively suppressed the secondary in vitro IgG antibody plaque-forming cell (PFC) response to the T-dependent antigen TNP-KLH but not to the T-independent antigens TNP-LPS and DNP-Lys-Ficoll. The suppression was antigen nonspecific. The mechanism of suppression occurred primarily through the activation of Lyt-1+, I-J+ suppressor-inducer cells, which in turn activated a Lyt-2+ suppressor T-cell population. The activity of preexisting, antigen-specific Lyt-2+ suppressor T cells was not influenced by SAP. The antigen-nonspecific suppressor T cells generated by SAP were sensitive to cyclophosphamide. Removal of SAP from the culture fluid with rabbit anti-Mo SAP antibody or agarose beads abrogated the suppression. Pentraxin proteins closely related to mouse SAP, such as human SAP and hamster female protein (FP), also displayed immunoregulatory activity of the antibody response by the same cellular mechanism. The results suggest that SAP regulates antibody responses by the activation of suppressor-inducer T cells and that the regulation of the antibody response during the acute stage of inflammation may occur via SAP.

Binding specificity of mouse serum amyloid P-component for fibronectin

Binding between purified mouse serum amyloid P-component (SAP) and plasma fibronectin (Fn) occurred when either one of the proteins was immobilized by specific antibody and the second protein was offered in a soluble form. Binding of Fn to immobilized SAP was cooperative and saturable at a molar ratio of SAP/Fn = 7.1. The molar ratio at saturation was 3.7 for SAP/Fn when SAP was allowed to bind to immobilized Fn. The binding required 2 to 3mM amounts of Ca++. The binding of SAP to Fn was selectively inhibited by a monoclonal antibody specific for the mid-molecule region of Fn, by soluble gelatin, and by heparin in the presence of 3mM Ca++. We conclude that the SAP binding site was localized at the mid-molecule region of Fn that includes the adjacent gelatin-binding domain and the heparin-I binding domain.