Satellite-DNA evolutionary patterns under a complex evolutionary scenario: the case of Acrolophus subgroup (Centaurea L., Compositae) from the western Mediterranean

Within the genus Centaurea (subtribe Centaureinae, tribe Cardueae, Compositae) hybridizations and reticulate-evolution phenomena have widely been recognized. This is especially true in the taxa included in the subgroup Acrolophus from the western Mediterranean area, in which recurrent hybridizations of parapatric ("microallopatric") lineages within the geographical range of a primary radiation have been suggested. The subgroup Acrolophus includes taxa from three sections (i.e. Acrolophus, Phalolepis and Willkommia), and, together with other subgroups, forms the named Jacea group (one of the three main groups into which Centaurea is divided). In this paper, we have studied the influence that the complex evolutionary scenario described for the Acrolophus subgroup from the western Mediterranean exerts on the evolutionary pattern of a satellite-DNA family, the HinfI family, which exists within the genomes of these taxa. To this end, we have analyzed the evolution of this satellite-DNA family in taxa from different taxonomic comparative levels: i) seven subspecies of the C. boissieri complex (one of which with two varieties) of the sect. Willkommia; ii) species of the sections Willkommia (10 species, 19 taxa), Acrolophus (two species), and Phalolepis (two species), all in the Acrolophus subgroup; iii) one external species to the Jacea group, C. granatensis from the group Acrocentron; iv) and species from other related genera from the Centaureinae subtribe (Phonus and Carthamus, both belonging to the Carthamus group). The influence of the suggested model for the origin and diversification of the Acrolophus subgroup is evidenced by the existence of three different HinfI satellite-DNA subfamilies coexisting in some genomes, and by the analysis that we have made by comparing site-by-site the transition stages in the process of concerted evolution between the sequences of the each subfamily. From this analysis, we can deduce that the HinfI repeated subfamilies evolved in a gradual manner, and that the different stages of concerted evolution fit quite well with the combined nuclear-chloroplast-DNA-deduced divergences and phylogeny of the subtribe Centaureinae. The HinfI satellite-DNA from the Carthamus species group (genera Carthamus and Phonus) and from the Acrocentron group (Centaurea granatensis) shows a high intraspecific conservation of the repeats, suggesting that the mechanisms producing concerted evolution have been efficient in these taxa. In addition, the comparison of individual nucleotide positions between related species shows a paucity in the spreading of variants in each subfamily with satellite-DNA divergence, an indication of a constant rate of homogenization of the repeated cluster. On the contrary, this trend is absent in the comparisons of the HinfI sequences from taxa of the subgroup Acrolophus. In this subgroup, we have found in this repetitive family similar representative average sequences for each taxon analyzed, polymorphic sites in each taxon being scant, most of them autapomorphic, representing early stages of genetic differentiation between taxa in the process of concerted evolution. The absence of concerted evolution was visualized by similar levels of intraspecific variation and interspecific divergence and by the lack of fixed species-diagnostic nucleotide sites. These facts might reflect the reticulate mode of evolution of Acrolophus.     

Satellite DNA as a phylogenetic marker: case study of three genera of the Murinae subfamily

Satellite DNA (satDNA) represent tens percent of any of the vertebrate genome. Still, a complete set of sat-DNA fragments is not determined for either species. It is known that some genus with species-specific modifications possess a satDNA characteristic for the genus. So, satDNA was used as a phylogenetic marker in some cases when precise satDNA fragment was cloned. We used the probe of the whole pericentromeric region and 4 cloned satDNA fragments of Mus musculus in order to consider probes value for phylogenesis of 3 Murinae genera. Fluorescent in situ hybridization (FISH) revealed similar pattern on metaphase spreads inside genus Mus, though some difference was noted. None of the satDNA fragment gave signal in the centromeric region on chromosomes from genera Sylvaemus and Apodemus. These data are in agreement with those on satDNA fragments in the genome determined by dot-blot hybridization: M musculus satDNA fragments are absent in the genomes of both remote genera while they are present in the genomes of the genera Mus, though in different amounts. SatDNA of each genera should be cloned for the phylogenetic purposes.     

High-throughput analysis of satellite DNA in the grasshopper <Emphasis Type="Italic">Pyrgomorpha conica</Emphasis> reveals abundance of homologous and heterologous higher-order repeats

Satellite DNA (satDNA) constitutes an important fraction of repetitive DNA in eukaryotic genomes, but it is barely known in most species. The high-throughput analysis of satDNA in the grasshopper Pyrgomorpha conica revealed 87 satDNA variants grouped into 76 different families, representing 9.4% of the genome. Fluorescent in situ hybridization (FISH) analysis of the 38 most abundant satDNA families revealed four different patterns of chromosome distribution. Homology search between the 76 satDNA families showed the existence of 15 superfamilies, each including two or more families, with the most abundant superfamily representing more than 80% of all satDNA found in this species. This also revealed the presence of two types of higher-order repeats (HORs), one showing internal homologous subrepeats, as conventional HORs, and an additional type showing non-homologous internal subrepeats, the latter arising by the combination of a given satDNA family with a non-annotated sequence, or with telomeric DNA. Interestingly, the heterologous subrepeats included in these HORs showed higher divergence within the HOR than outside it, suggesting that heterologous HORs show poor homogenization, in high contrast with conventional (homologous) HORs. Finally, heterologous HORs can show high differences in divergence between their constituent subrepeats, suggesting the possibility of regional homogenization.     

Identification and genetic mapping of random amplified polymorphic DNA (RAPD) markers to the sheep genome

The random amplified polymorphic DNA (RAPD) assay utilizes the polymerase chain reaction (PCR) and short primers of arbitrary nucleotide sequence to amplify DNA. In this study, the RAPD assay was used to identify and map polymorphic markers in the AgResearch International Mapping Flock (IMF) sheep pedigrees. Sires and dams of eight of the full-sib IMF pedigrees were screened with 131 different 10-mer oligonucleotide primers. An average of 85 RAPD polymorphisms was identified between each parental pair, and 53 markers were contributed to the AgResearch IMF collaboration. Forty-five of the RAPD markers were mapped in the AgResearch IMF genetic linkage map, and at least one marker was located on 17 of the 26 autosomes and both sex chromosomes. Three lines of evidence were used to check for the homology of scored polymorphisms in different pedigrees, pedigree evaluation, segregation analysis, and Southern blot analysis. These results demonstrate that the RAPD assay is a powerful approach for identifying polymorphisms that can be used as markers for constructing a sheep genetic linkage map. Received: 5 October 1995 / Accepted: 16 April 1996     

Quantitative trait nucleotide analysis using Bayesian model selection

Although much attention has been given to statistical genetic methods for the initial localization and fine mapping of quantitative trait loci (QTLs), little methodological work has been done to date on the problem of statistically identifying the most likely functional polymorphisms using sequence data. In this paper we provide a general statistical genetic framework, called Bayesian quantitative trait nucleotide (BQTN) analysis, for assessing the likely functional status of genetic variants. The approach requires the initial enumeration of all genetic variants in a set of resequenced individuals. These polymorphisms are then typed in a large number of individuals (potentially in families), and marker variation is related to quantitative phenotypic variation using Bayesian model selection and averaging. For each sequence variant a posterior probability of effect is obtained and can be used to prioritize additional molecular functional experiments. An example of this quantitative nucleotide analysis is provided using the GAW12 simulated data. The results show that the BQTN method may be useful for choosing the most likely functional variants within a gene (or set of genes). We also include instructions on how to use our computer program, SOLAR, for association analysis and BQTN analysis.     

The clustering of four subfamilies of satellite DNA at individual chromosome ends in Silene latifolia.

The satellite DNA (satDNA) on the ends of chromosomes has been isolated and characterized in the dioecious plant Silene latifolia. BAC clones containing large numbers of repeat units of satDNA in a tandem array were isolated to examine the clustering of the repeat units. satDNA repeat units were purified from each isolated BAC clone and sequenced. To investigate pairwise similarities among the repeat units, a phylogenetic tree was constructed using the neighbor-joining algorithm. The repeat units derived from 7 BAC clones were grouped into SacI, KpnI, #11F02, and #16E07 subfamilies. The SacI and KpnI subfamilies have been reported previously. Multicolored fluorescence in situ hybridization (FISH) using SacI or KpnI subfamily probes resulted in different signal intensities and locations at the chromosomal ends, indicating that each chromosomal end has a unique composition of subfamilies of satDNA. For example, the p arm of the X chromosome exhibited signal composition similar to that on the pseudo autosomal region (PAR) of the Y chromosome, but not to that on the q arm of the X chromosome. The satDNA has not been completely homogenized in the S. latifolia genome. Each subfamily is available for a probe of FISH karyotyping.     

Comparative performance of double‐digest RAD sequencing across divergent arachnid lineages

Next‐generation sequencing technologies now allow researchers of non‐model systems to perform genome‐based studies without the requirement of a (often unavailable) closely related genomic reference. We evaluated the role of restriction endonuclease (RE) selection in double‐digest restriction‐site‐associated DNA sequencing (ddRADseq) by generating reduced representation genome‐wide data using four different RE combinations. Our expectation was that RE selections targeting longer, more complex restriction sites would recover fewer loci than RE with shorter, less complex sites. We sequenced a diverse sample of non‐model arachnids, including five congeneric pairs of harvestmen (Opiliones) and four pairs of spiders (Araneae). Sample pairs consisted of either conspecifics or closely related congeneric taxa, and in total 26 sample pair analyses were tested. Sequence demultiplexing, read clustering and variant calling were performed in the pyRAD program. The 6‐base pair cutter EcoRI combined with methylated site‐specific 4‐base pair cutter MspI produced, on average, the greatest numbers of intra‐individual loci and shared loci per sample pair. As expected, the number of shared loci recovered for a sample pair covaried with the degree of genetic divergence, estimated with cytochrome oxidase I sequences, although this relationship was non‐linear. Our comparative results will prove useful in guiding protocol selection for ddRADseq experiments on many arachnid taxa where reference genomes, even from closely related species, are unavailable.     

Acrocentric chromosome associations in man.

Heterogeneity among chromosomes was found to be a highly significant source of variation for association proportions, while culture, slide, and observer were negligible sources of variation for association proportions although important for numbers of associations. The consequences of these results for tests of group differences are discussed. It seems evident that each pair of acrocentric chromosomes has its own characteristic probability of entering into association. This is presumably a combination of the probability for each individual member of the pair, a proposition easily tested utilizing acrocentric chromosomes carrying polymorphisms which allow each member of the pair to be individually recognized. A mathematical theory for pairwise satellite association was developed and shown to fit observations on banded chromosomes. While we found very significant heterogeneity among individuals in the frequency with which different chromosomes entered into associations, there was no significant evidence for preferential association between any particular chromosomes, either heterologous or homologous. This finding in our material of apparently random associations between different chromosomes is contrary to claims made by other investigators and should be tested on other material. No correlation was found between the phenotype of the chromosome, as judged by cytogenetic polymorphisms, and its probability of association.     

Genetic and environmental influences on alcohol use: DF analysis of NLSY kinship data

Research designs to study alcohol use and abuse have included twin, adoption and family history/high risk studies. Results have consistently implied a genetic factor in the aetiology of alcohol abuse. However, less research has been conducted in search of environmental factors. This study uses kinship structure in a large national dataset (the National Longitudinal Survey of Youth) to estimate (using DeFries-Fulker analysis) the extent of the shared genetic, non-shared genetic, shared environmental and non-shared environmental influences on alcohol use. The NLSY kinship sample contained 3890 pairs of cousins, half-siblings, full-siblings and twins between the ages of 14 and 21 in the initial year of the survey (1979). Estimates of heritability (h2) and shared environment (c2) were small to moderate for the entire dataset for both light drinking and heavy drinking behaviour, with h2 estimates slightly higher in each case. Non-shared genetic measures of self-esteem and locus of control accounted for a significant portion of the remaining variance in heavy drinking behaviour. Race and gender patterns showed c2 and h2 estimates that were also small to moderate for both light and heavy drinking behaviour. Significant non-shared effects were found for the White group for heavy drinking behaviour, and for male pairs for both heavy and light drinking behaviour. Additionally, implications and future directions are discussed.     

Harmonization of the multiple-locus variable-number tandem repeat analysis method between Denmark and Norway for typing Salmonella Typhimurium isolates and closer examination of the VNTR loci

AIMS: Harmonization and evaluation of the multiple-locus variable-number tandem repeat analysis (MLVA) method for sub-typing Salmonella enterica ssp. enterica serovar Typhimurium (Salm. Typhimurium) in Denmark and Norway, and analysis of the typing data. METHODS AND RESULTS: The Salm. Typhimurium MLVA (STMLVA) method, which uses length polymorphisms in five tandem-repeated DNA loci to differentiate isolates, was harmonized between Denmark and Norway, using a common set of 14 isolates. The MLVA assay that is routinely used at the Norwegian Institute of Public Health was set up at the Statens Serums Institute. Both the institutes used an ABI-310 Genetic Analyzer for capillary separation of PCR products, and the same internal size standard. Running the same set of 14 test isolates in both countries and comparing the results showed an excellent typing match at all loci in all isolates. Subsequently, 461 isolates were genotyped in Norway and 454 isolates were genotyped in Denmark. The STMLVA assay displayed a large number of allelic profiles that were distinct for each country as well as shared profiles. Differences in variable number of tandem repeats allele frequencies and absence of amplification products were observed between Denmark and Norway. CONCLUSIONS: The MLVA method was set up in two different laboratories and produced completely matching typing data that could be shared rapidly by e-mail for comparison. Notably, differences in allele frequencies and absence of amplification were noted between the countries. SIGNIFICANCE AND IMPACT OF THE STUDY: The STMLVA method was shown to be easily implemented and to produce typing data, which were shared over the Internet. This enables increased speed of typing and comparison of data between countries, when compared with earlier typing methods. Information embedded in the allele frequencies might give clues to the origin and source of isolates.     

Disparate molecular evolution of two types of repetitive DNAs in the genome of the grasshopper Eyprepocnemis plorans

Wide arrays of repetitive DNA sequences form an important part of eukaryotic genomes. These repeats appear to evolve as coherent families, where repeats within a family are more similar to each other than to other orthologous representatives in related species. The continuous homogenization of repeats, through selective and non-selective processes, is termed concerted evolution. Ascertaining the level of variation between repeats is crucial to determining which evolutionary model best explains the homogenization observed for these sequences. Here, for the grasshopper Eyprepocnemis plorans, we present the analysis of intragenomic diversity for two repetitive DNA sequences (a satellite DNA (satDNA) and the 45S rDNA) resulting from the independent microdissection of several chromosomes. Our results show different homogenization patterns for these two kinds of paralogous DNA sequences, with a high between-chromosome structure for rDNA but no structure at all for the satDNA. This difference is puzzling, considering the adjacent localization of the two repetitive DNAs on paracentromeric regions in most chromosomes. The disparate homogenization patterns detected for these two repetitive DNA sequences suggest that several processes participate in the concerted evolution in E. plorans, and that these mechanisms might not work as genome-wide processes but rather as sequence-specific ones.     

Simulation analysis of muscle activity changes with altered body orientations during pedaling

Testing hypotheses related to the effect of gravitational orientation on neural control mechanisms is difficult for most locomotor tasks, like walking, because body orientation with respect to gravity affects both sensorimotor control and task mechanics. To examine the mechanical effect of body orientation independently from changes in workload and posture, Brown et al. (J. Biomech. 29 p. 1349, 1996) studied pedaling at altered body orientations. They found that subjects pedaling at different orientations changed needlessly their muscle excitations, putatively to preserve body-upright pedaling kinematics. We tested the feasibility of this hypothesis using simulations based on a three biomechanical-function pair organization for control of lower limb muscles (limb extension/flexion pair, extension/flexion transition pair, and foot plantarflexion/dorsiflexion pair), where each pair consists of alternating agonistic/antagonistic muscles. Adjustment of only three parameters, one to scale the muscle excitations of each pair, was sufficient to preserve pedaling kinematics to altered body orientation. Because these adjustments produced changes in muscle excitation and net joint moments similar to those observed in pedaling subjects, the hypothesis is supported. Moreover, the effectiveness of a decoupled gain adjustment procedure where each parameter was adjusted by error in only one aspect of the pedaling trajectory during each iteration (i.e., cadence adjusted the Ext/Flex parameter; peak-to-peak variation in crank velocity over the cycle adjusted the transition parameter; average ankle angle over the cycle adjusted the foot parameter) further supports the distinct function of each muscle pair.     

Concerted evolution of satellite DNA in Sarcocapnos: a matter of time

SarkOne is a genus-specific satellite-DNA family, isolated from the genomes of the species of the genus Sarcocapnos. This satellite DNA is composed of repeats with a consensus length of 855 bp and a mean G+C content of 52.5%. We have sequenced a total of 189 SarkOne monomeric repeats belonging to a total of seven species of the genus Sarcocapnos. The comparative analysis of these sequences both at the intraspecific and the interspecific levels have revealed divergence patterns between species are proportional to between-species divergence according to the phylogeny of the genus. Our study demonstrates that the molecular drive leading to the concerted-evolution pattern of this satellite DNA is a time-dependent process by which new mutations are spreading through genomes and populations at a gradual pace. However, time is a limiting factor in the observation of concerted evolution in some pairwise comparisons. Thus, pairwise comparisons of species sharing a recent common ancestor did not reveal nucleotide sites in transitional stages higher than stage III according to the Strachan's model. By contrast, there was a gradation in the percentage of upper transition stages (IV, V, VI) the more phylogenetically distant the species were. In addition, closely related species shared a high number of polymorphic sites, but these types of sites were not common when comparing more distant species. All these data are discussed in the light of current life-cycle models of satellite-DNA evolution.     

DNA profiling of cattle using micro- and minisatellite core probes

We have evaluated 15 different micro- and minisatellite core probes for use in identity and paternity testing in cattle, based on Southern blot hybridization analysis. The core probes were tested in animals of different breeds and by analysis of seven two-generation pedigrees. Of the 15 core probes tested, seven were able to detect on average seven variant bands per individual animal. Segregation analysis showed that on average two out of 3 6 variant bands scored per core probe were genetically linked while two out of 12 variant bands correspond to the same allelic pair. The results obtained demonstrate the effectiveness of multilocus core probes for determining identity and paternity in cattle.     

DNA repair gene polymorphisms, pre-natal factors and the frequency of somatic mutations in the glycophorin-A gene among healthy newborns

This study investigates variation in somatic mutation frequency, as measured by the glycophorin-A (GPA) somatic mutation assay, in relation to polymorphic variation among 435 newborn babies in DNA repair genes XRCC1, XRCC3 and XRCC4 and gender, parental age, social class and smoking habits. The three polymorphisms under investigation were an Arg --> Gln substitution at codon 399 in exon 10 of XRCC1, a Thr --> Met substitution at codon 241 in exon 7 of XRCC3 and an Ile --> Thr substitution at codon 401 in exon 4 of XRCC4. The study population is an extension of that previously analysed for GPA mutations and XRCC1 polymorphisms. A significant difference was seen in the earlier work in the genotype distribution for the XRCC1 Arg399Gln polymorphism between the main population and the small number with extreme values for NN variant frequency and this was maintained in the larger study group (OR 3.20 [95% CI: 1.16, 8.81]) P = 0.043). No such association was seen for XRCC3 or XRCC4 polymorphisms. When adjustments were made for multiple testing, neither N0 nor NN variant frequencies in the main study population were found to be influenced by the polymorphisms in XRCC1, XRCC3, or XRCC4. In addition, neither maternal or paternal smoking, age or social class nor the gender of the offspring were found to affect variant frequencies nor were variant frequencies influenced by any interaction between any of these factors and genotype. It is concluded that the genotypic variation in DNA repair genes examined in this study has no discernable effect on the genesis of the somatic mutations observed at birth.     

Evidence of Extensive Genetic Exchange in the Rp49 Region among Polymorphic Chromosome Inversions in Drosophila Subobscura

Restriction map variation in 107 lines extracted from two natural populations of Drosophila subobscura was investigated with seven four-nucleotide-recognizing enzymes in a 1.6-kb region including the rp49 gene, that is located very close to the proximal breakpoint of inversion O3. Fourteen restriction site and 8 length polymorphisms, resulting in 73 haplotypes, have been identified. Estimated heterozygosity per nucleotide, pi = 0.0045, is comparable to the average nucleotide variation observed in Drosophila melanogaster. Because of the location of the rp49 region in D. subobscura, variation in three different gene arrangements-Ost, O3 + 4 and O3 + 4 + 8-has been compared. Out of 14 restriction site polymorphisms, 3 are shared by Ost, O3 + 4 and O3 + 4 + 8, and 3 additional ones are shared by Ost and O3 + 4, evidencing extensive genetic exchange among these polymorphic inversions. In agreement with previous data, the higher level of variation of O3 + 4 (as measured by haplotype diversity and nucleotide variation) suggests that O3 + 4 may be ancestral in relationship to extant gene arrangements.     

Recurrent amplifications and deletions of satellite DNA accompanied chromosomal diversification in South American tuco-tucos (genus Ctenomys, Rodentia: Octodontidae): a phylogenetic approach

We investigated the relationship between satellite copy number and chromosomal evolution in tuco-tucos (genus Ctenomys), a karyotypically diverse clade of rodents. To explore phylogenetic relationships among 23 species and 5 undescribed forms, we sequenced the complete mitochondrial cytochrome b genes of 27 specimens and incorporated 27 previously published sequences. We then used quantitative dot-blot techniques to assess changes in the copy number of the major Ctenomys satellite DNA (satDNA), named RPCS. Our analysis of the relationship between variation in copy number of RPCS and chromosomal changes employed a maximum-likelihood approach to infer the copy number of the satellite RPCS in the ancestors of each clade. We found that amplifications and deletions of RPCS were associated with extensive chromosomal rearrangements even among closely related species. In contrast, RPCS copy number stability was observed within clades characterized by chromosomal stability. This example reinforces the suspected role of amplification, deletion, and intragenomic movement of satDNA in promoting extensive chromosomal evolution.     

The Complex Satellite DNA of Tropaeolum majus L.: Partial Characterization of Isolated and of Cloned Restriction Fragments

Satellite DNA (satDNA) was purified by repeated neutral CsCl,ethidium bromide/CsCl and actinomycin D/CsCl density centrifugationfrom total nuclear DNA of Tropaeolum majus. Digestion patternsof satDNA and main band DNA as generated with 22 different restrictionenzymes were partially characterized and hybridized by the Southernblot technique with Hpa II-generated satDNA fragments and aribosomal DNA fragment. Some restriction fragments were sequencedby the chemical method, either directly, or after cloning, andpossible secondary structures were determined. The results showthat the satellite is of high complexity and evidently composedof different, interspersed repeats, and is also interspersedwith ribosomal sequences. Some sequences of the satellite aredispersed throughout the Tropaeolum genome, and even found inthe chloroplast genome. Most of the restriction enzymes cutthe satDNA into many fragments of lengths between 14 bp and3000 bp. Hpa II cut the satellite DNA into at least 63 differentsized fragments (more than is known from any other plant satDNA).Sal I cut the satDNA into a single fragment of 1040 bp in size,which probably represented the superrepeat unit. Sequence analysisof satDNA restriction fragments and of cloned fragments isolatedat different times, indicated a rapid diversification in vivoand in vitro. Computer modeling of most likely secondary structuressuggest the occurrence of palindromic loops (cruciform structures).These could be the basis of rapid diversification in being sitesof preferred intragenomic recombination and rearrangement. Cloning, palindromic sequences, restriction analysis, satellite DNA complexity, Tropaeolum majus L, nasturtium     

Specificity of SAF-A and lamin B binding in vitro correlates with the satellite DNA bending state

There is evidence that Matrix Attachment Region (MAR)-binding proteins also bind satellite DNA (satDNA). The aim of the current work was to determine whether the major nuclear matrix (NM) MAR-binding proteins are able to recognize satDNAs of different locations and what DNA structural features are important for the recognition. In nuclei and NM, a number of the same polypeptides were recognized on a southwestern blot when MAR of immunoglobulin kappa gene (Ig kappa MAR) and pericentromeric (periCEN) satDNA fragments were used. However, the binding decreased dramatically when human and mouse CEN satDNA were used for the probes. After an NM extract was subjected to ion exchange chromatography, the main DNA-binding proteins were identified as SAF-A (scaffold attachment factor A) and lamin B. It was not possible to test the binding of lamin B by gel mobility shift assay (GMSA), but SAF-A showed an ability to distinguish CEN and periCEN satDNA fragments in GMSA. While periCEN fragments have an abnormally slow mobility on electrophoresis, which is a hallmark of bent DNA, CEN satDNA fragments have a normal mobility. A computer analysis was done using the wedge model (Ulanovsky and Trifonov [1987] Nature 326:720-722), which describes how the curved state depends on particular nucleotide sequences. The curved states of the fragments predicted by the model are in good agreement with their ability to be recognized by NM proteins. Thus SAF-A and lamin B are able to recognize conserved structural features of satDNA in the same way that MAR-binding proteins recognize MARs in spite of a lack of a consensus sequence. CEN and periCEN satDNAs are distinguished by proteins in correlation with the helical curvature of these fragments.