Organization and evolution of alpha satellite DNA from human chromosome 11

The human alpha satellite repetitive DNA family is organized as distinct chromosomal subsets located at the centromeric regions of each human chromosome. Here, we describe a subset of the alpha satellite which is localized to human chromosome 11. The principal unit of repetition of this alpha satellite subset is an 850 bp XbaI fragment composed of five tandem diverged alphoid monomers, each 171 bp in length. The pentamer repeat units are themselves tandemly reiterated, present in 500 copies per chromosome 11. In filter hybridization experiments, the Alpha 11 probes are specific for the centromeric alpha satellite sequences of human chromosome 11. The complete nucleotide sequences of two independent copies of the XbaI pentamer reveal a pentameric configuration shared with the alphoid repeats of chromosomes 17 and X, consistent with the existence of an ancestral pentameric repeat common to the centromeric arrays of at least these three human chromosomes.     

Segmental amplification in a satellite DNA: Restriction enzyme analysis of the major satellite ofMacropus rufogriseus

The 1.708 g/cc satellite DNA of the red necked wallaby is shown to consist of a number of related families of sequences arranged in tandem arrays. Particular families are subpopulations of other families; their distribution supports a model of successive amplification events during the generation of the satellite. In each amplification episode one 2,500 bp unit is multiplied into a tandemly repeated array of that unit (segmental amplification). The 1.708 g/cc sequences can be detected in related kangaroo species in much reduced amount, and with changes to the long order periodicity of the repeat units.     

Genomic organization of alpha satellite DNA on human chromosome 7: evidence for two distinct alphoid domains on a single chromosome.

A complete understanding of chromosomal disjunction during mitosis and meiosis in complex genomes such as the human genome awaits detailed characterization of both the molecular structure and genetic behavior of the centromeric regions of chromosomes. Such analyses in turn require knowledge of the organization and nature of DNA sequences associated with centromeres. The most prominent class of centromeric DNA sequences in the human genome is the alpha satellite family of tandemly repeated DNA, which is organized as distinct chromosomal subsets. Each subset is characterized by a particular multimeric higher-order repeat unit consisting of tandemly reiterated, diverged alpha satellite monomers of approximately 171 base pairs. The higher-order repeat units are themselves tandemly reiterated and represent the most recently amplified or fixed alphoid sequences. We present evidence that there are at least two independent domains of alpha satellite DNA on chromosome 7, each characterized by their own distinct higher-order repeat structure. We determined the complete nucleotide sequences of a 6-monomer higher-order repeat unit, which is present in approximately 500 copies per chromosome 7, as well as those of a less-abundant (approximately 10 copies) 16-monomer higher-order repeat unit. Sequence analysis indicated that these repeats are evolutionarily distinct. Genomic hybridization experiments established that each is maintained in relatively homogeneous tandem arrays with no detectable interspersion. We propose mechanisms by which multiple unrelated higher-order repeat domains may be formed and maintained within a single chromosomal subset.     

Concerted evolution of primate alpha satellite DNA. Evidence for an ancestral sequence shared by gorilla and human X chromosome alpha satellite

To understand evolutionary events in the formation of higher-order repeat units in alpha satellite DNA, we have examined gorilla sequences homologous to human X chromosome alpha satellite. In humans, alpha satellite on the X chromosome is organized as a tandemly repeated, 2.0 x 10(3) base-pairs (bp) higher-order repeat unit, operationally defined by the restriction enzyme BamHI. Each higher-order repeat unit is composed of 12 tandem approximately 171 base-pair monomer units that have been classified into five distinct sequence homology groups. BamHI-digested gorilla genomic DNA hybridized with the cloned human 2 x 10(3) bp X alpha satellite repeat reveals three bands of sizes approximately 3.2 x 10(3), 2.7 x 10(3) and 2 x 10(3) bp. Multiple copies of all three repeat lengths have been isolated and mapped to the centromeric region of the gorilla X chromosome by fluorescence in situ hybridization. Long-range restriction mapping using pulsed-field gel electrophoresis shows that the 2.7 x 10(3) and 3.2 x 10(3) bp repeat arrays exist as separate but likely neighboring arrays on the gorilla X, each ranging in size from approximately 200 x 10(3) to 500 x 10(3) bp, considerably smaller than the approximately 2000 x 10(3) to 4000 x 10(3) bp array found on human X chromosomes. Nucleotide sequence analysis has revealed that monomers within all three gorilla repeat units can be classified into the same five sequence homology groups as monomers located within the higher-order repeat unit on the human X chromosome, suggesting that the formation of the five distinct monomer types predates the divergence of the lineages of contemporary humans and gorillas. The order of 12 monomers within the 2 x 10(3) and 2.7 x 10(3) bp repeat units from the gorilla X chromosome is identical with that of the 2 x 10(3) bp repeat unit from the human X chromosome, suggesting an ancestral linear arrangement and supporting hypotheses about events largely restricted to single chromosome types in the formation of alpha satellite higher-order repeat units.     

Heterochromatin and highly repeated DNA sequences in rye (Secale cereale)

Secale cereale DNA, of mean fragment length 500 bp, was fractionated by hydroxylapatite chromatography to allow recovery of a very rapidly renaturing fraction (C₀t 0–0.02). This DNA fraction was shown to contain several families of highly repeated sequence DNA. Two highly repeated families were purified; (1) a fraction which renatured to a density of 1.701 g/ cc and comprised 2–4% of the total genome, and (2) polypyrimidine tract DNA which comprised 0.1% of the total genome. The 1.701 g/cc DNA consisted of short sequence repeat units (5–50 bp long) tandemly repeated in blocks 30 kb long, while a portion of the polypyrimidine tract DNA behaved as part of a much larger block of tandemly repeated sequences. The chromosomal location of these sequences was determined by the in situ hybridisation of radioactive, complementary RNA to root tip mitotic chromosomes and showed the 1.701 g/cc sequences to be largely limited to the telomeric blocks of heterochromatin, accounting for 25–50% of the DNA present in these parts of the chromosomes. The polypyrimidine tracts were distributed at interstitial locations with 20–30% of the sequences at three well defined sites. The combined distributions of the 1.701 g/cc DNA sequences and polypyrimidine tracts effectively individualised each rye chromosome thus providing a sensitive means of identifying these chromosomes. The B chromosomes present in Secale cereale cv. Unevita, did not show defined locations for the sequences analysed. — The data are discussed in terms of the structure of the rye genome and the generality of the observed genomic arrangement of highly repeated sequence DNA.     

Chromosome-specific subsets of human alpha satellite DNA: Analysis of sequence divergence within and between chromosomal subsets and evidence for an ancestral pentameric repeat

Summary The centromeric regions of human chromosomes are characterized by diverged chromosome-specific subsets of a tandemly repeated DNA family, alpha satellite, which is based on a fundamental monomer repeat unit 171 bp in length. We have compared the nucleotide sequences of 44 alphoid monomers derived from cloned representatives of the multimeric higher-order repeat units of human chromosomes 1, 11, 17, and X. The 44 monomers exhibit an average 16% divergence from a consensus alphoid sequence, and can be assigned to five distinct homology groups based on patterns of sequence substitutions and gaps relative to the consensus. Approximately half of the overall sequence divergence can be accounted for by sequence changes specific to a particular homology group; the remaining divergence appears to be independent of the five groups and is randomly distributed, both within and between chromosomal subsets. The data are consistent with the proposal that the contemporary tandem arrays on chromosomes 1, 11, 17, and X derive from a common multimeric repeat, consisting of one monomer each from the five homology groups. The sequence comparisons suggest that this pentameric repeat must have spread to these four chromosomal locations many millions of years ago, since which time evolution of the four, now chromosome-specific, alpha satellite subsets has been essentially independent.     

Chromosome specificity of satellite DNAs: short- and long-range organization of a diverged dimeric subset of human alpha satellite from chromosome 3

The human alpha satellite DNA family, like many highly repeated satellite DNAs in eukaryotic genomes, is organized in distinct chromosome-specific subsets. As part of investigations into the molecular and evolutionary basis for the chromosome-specific nature of such subsets, we report the isolation and characterization of alpha satellite sequences specific for human chromosome 3. This subset is characterized by a predominant tandemly arranged 2.9 kb higher-order repeat unit which, in turn, consists of 17 tandem diverged monomer repeat units of 171 bp. Nucleotide sequence analysis reveals that the chromosome 3 higher-order repeat units are comprised, at least in part, of diverged dimeric ( 340 bp) sub-repeats and that this divergence accounts for the chromosome-specific behavior of this subset. Pulsed-field gel electrophoresis demonstrates that the chromosome 3 higher-order repeat units are localized in large domains, at least 1000 kb in length. Familial restriction fragment length polymorphisms associated with the satellite subset can be detected by pulsed field gel electrophoresis and may facilitate molecular analysis of interchromosomal variation.     

A molecular and cytogenetic survey of major repeated DNA sequences in tomato (Lycopersicon esculentum)

Summary The major families of repeated DNA sequences in the genome of tomato (Lycopersicon esculentum) were isolated from a sheared DNA library. One thousand clones, representing one million base pairs, or 0.15% of the genome, were surveyed for repeated DNA sequences by hybridization to total nuclear DNA. Four major repeat classes were identified and characterized with respect to copy number, chromosomal localization by in situ hybridization, and evolution in the family Solanaceae. The most highly repeated sequence, with approximately 77000 copies, consists of a 162 bp tandemly repeated satellite DNA. This repeat is clustered at or near the telomeres of most chromosomes and also at the centromeres and interstitial sites of a few chromosomes. Another family of tandemly repeated sequences consists of the genes coding for the 45 S ribosomal RNA. The 9.1 kb repeating unit in L. esculentum was estimated to be present in approximately 2300 copies. The single locus, previously mapped using restriction fragment length polymorphisms, was shown by in situ hybridization as a very intense signal at the end of chromosome 2. The third family of repeated sequences was interspersed throughout nearly all chromosomes with an average of 133 kb between elements. The total copy number in the genome is approximately 4200. The fourth class consists of another interspersed repeat showing clustering at or near the centromeres in several chromosomes. This repeat had a copy number of approximately 2100. Sequences homologous to the 45 S ribosomal DNA showed cross-hybridization to DNA from all solanaceous species examined including potato, Datura, Petunia, tobacco and pepper. In contrast, with the exception of one class of interspersed repeats which is present in potato, all other repetitive sequences appear to be limited to the crossing-range of tomato. These results, along with those from a companion paper (Zamir and Tanksley 1988), indicate that tomato possesses few highly repetitive DNA sequences and those that do exist are evolving at a rate higher than most other genomic sequences.     

Characterisation of a boundary between satellite III and alphoid sequences on human chromosome 10.

Alphoid and satellite III sequences are arranged as large tandem arrays in the centromeric regions of human chromosomes. Several recent studies using in situ hybridisation to investigate the relative positions of these sequences have shown that they occupy adjacent but non-overlapping domains in metaphase chromosomes. We have analysed the DNA sequence at the junction between alphoid and satellite III sequences in a cosmid previously mapped to chromosome 10. The alphoid sequence consists of tandemly arranged dimers which are distinct from the known chromosome 10-specific alphoid family. Polymerase chain reaction experiments confirm the integrity of the sequence data. These results, together with pulsed field gel electrophoresis data place the boundary between alphoid and satellite III sequences in the mapping interval 10 centromere-10q11.2. The sequence data shows that these repetitive sequences are separated by a partial L1 interspersed repeat sequence less than 500bp in length. The arrangement of the junction suggests that a recombination event has brought these sequences into close proximity.     

Highly repetitive DNA sequences that are restricted to the germ line in the hagfish Eptatretus cirrhatus: a mosaic of eliminated elements

The New Zealand hagfish, Eptatretus cirrhatus, is known to eliminate parts of its chromosomes during embryogenesis from presumptive somatic cells. Electrophoresis of germ line and somatic DNAs of this species, after treatment with the restriction endonucleases DraI and EcoRI, revealed three fragments of DNA that were restricted to the germ line. DNA filter hybridization experiments demonstrated that these fragments were present almost exclusively in the germ line DNA of E. cirrhatus and that they were highly and tandemly repeated. Thus, these DNA fragments appeared to be eliminated during embryogenesis. Moreover, one fragment (a DraI fragment) cross-hybridized with the germ line DNA from other species of hagfish, namely, Eptatretus okinoseanus and Paramyxine atami. Molecular cloning and sequence analysis revealed that the DraI fragment was composed mainly of closely related sequences of 85 bp in length and that this sequence was about 75% homologous to the sequence of EEEo2 (eliminated element of E. okinoseanus 2) which is a germ line-restricted and highly repetitive sequence that was isolated previously from E. okinoseanus. The other two fragments were composed of three families of closely related sequences that were 172 bp long (designated EEEc1), 61 bp long (EEEc2) and 54 bp long (EEEc3). Fluorescence in situ hybridization experiments revealed that each eliminated element was distributed on several chromosomes that are limited to germ cells. EEEo2 was dispersed on 12 C-band-positive chromosomes. EEEc1 and EEEc3 were dispersed on all C-band-positive and several C-band-negative chromosomes. By contrast, EEEc2 was located to terminal regions of several C-band-negative chromosomes. These results suggest that the eliminated chromosomes in hagfish are mosaics of highly repeated, germ line-restricted families of DNA sequences. Received: ██; in revised form: 25 October 1997 / Accepted: ██     

Interhomologue sequence variation of alpha satellite DNA from human chromosome 17: Evidence for concerted evolution along haplotypic lineages

Alpha satellite DNA is a family of tandemly repeated DNA found at the centromeres of all primate chromosomes. Different human chromosomes 17 in the population are characterized by distinct alpha satellite haplotypes, distinguished by the presence of variant repeat forms that have precise monomeric deletions. Pairwise comparisons of sequence diversity between variant repeat units from each haplotype show that they are closely related in sequence. Direct sequencing of PCR-amplified alpha satellite reveals heterogeneous positions between the repeat units on a chromosome as two bands at the same position on a sequencing ladder. No variation was detected in the sequence and location of these heterogeneous positions between chromosomes 17 from the same haplotype, but distinct patterns of variation were detected between chromosomes from different haplotypes. Subsequent sequence analysis of individual repeats from each haplotype confirmed the presence of extensive haplotype-specific sequence variation. Phylogenetic inference yielded a tree that suggests these chromosome 17 repeat units evolve principally along haplotypic lineages. These studies allow insight into the relative rates and/or timing of genetic turnover processes that lead to the homogenization of tandem DNA families. Correspondence to: H.F. Willard     

Identification of two families of satellite-like repetitive DNA sequences from the zebrafish (Brachydanio rerio)

To further our understanding of the structure and organization of the zebrafish genome, we have undertaken the analysis of highly and middle-repetitive DNA sequences. We have cloned and sequenced two families of tandemly repeated DNA fragments. The monomer units of the Type I satellite-like sequence are 186 bp long, A+T-rich (65%), and exhibit a high degree of sequence conservation. The Type I satellite-like sequence constitutes 8% of the zebrafish genome, or approximately 8 × 10⁵ copies per haploid genome. Southern analysis of genomic DNA, digested with several restriction endonucleases, shows a ladder of hybridizing bands, consistent with a tandem array, and suggests longer range periodic variations in the sequence of the tandem repeats. The Type II satellite has a monomer length of 165 bp, is also A+T-rich (68%), and constitues 0.2% of the zebrafish genome (22,000 copies per haploid genome). Southern analysis reveals a complex pattern rather than a ladder of regularly spaced hybridizing bands.     

Structure of DNA near long tandem arrays of alpha satellite DNA at the centromere of human chromosome 7.

The centromeric regions of human chromosomes contain long tracts of tandemly repeated DNA, of which the most extensively characterized is alpha satellite. In a screen for additional centromeric DNA sequences, four phage clones were obtained which contain alpha satellite as well as other sequences not usually found associated with tandemly repeated alpha satellite DNA, including L1 repetitive elements, an Alu element, and a novel AT-rich repeated sequence. The alpha satellite DNA contained within these clones does not demonstrate the higher-order repeat structure typical of tandemly repeated alpha satellite. Two of the clones contain inversions; instead of the usual head-to-tail arrangement of alpha satellite monomers, the direction of the monomers changes partway through each clone. The presence of both inversions was confirmed in human genomic DNA by polymerase chain reaction amplification of the inverted regions. One phage clone contains a junction between alpha satellite DNA and a novel low-copy repeated sequence. The junction between the two types of DNA is abrupt and the junction sequence is characterized by the presence of runs of A's and T's, yielding an overall base composition of 65% AT with local areas > 80% AT. The AT-rich sequence is found in multiple copies on chromosome 7 and homologous sequences are found in (peri)centromeric locations on other human chromosomes, including chromosomes 1, 2, and 16. As such, the AT-rich sequence adjacent to alpha satellite DNA provides a tool for the further study of the DNA from this region of the chromosome. The phage clones examined are located within the same 3.3-Mb SstII restriction fragment on chromosome 7 as the two previously described alpha satellite arrays, D7Z1 and D7Z2. These new clones demonstrate that centromeric repetitive DNA, at least on chromosome 7, may be more heterogeneous in composition and organization than had previously been thought.     

Germ line-restricted,highly repeated DNA sequences and their chromosomal localization in a Japanese hagfish (Eptatretus okinoseanus)

The various species of Japanese hagfish, namely, Eptatretus okinoseanus (types A and B), Eptatretus burgeri and Myxine garmani, are known to eliminate a fraction of their chromosomes during early embryogenesis. High molecular weight DNA from germ line cells and somatic cells of these hagfish species was isolated and digested with different restriction enzymes. The DNA fragments were separated by agarose gel electrophoresis. Digestion with BamHI and DraI generated two weak bands and one weak band, respectively, that were estimated to be about 90, and 180 bp and about 90 bp long and were limited to the germ line DNA in both types of E. okinoseanus. DNA filter hybridization experiments showed that the two BamHI fragments and the one DraI fragment were present almost exclusively in the germ line DNA of E. okinoseanus. Thus, these DNA fragments appear to be eliminated during embryogenesis. Moreover, evidence was obtained that these fragments are highly and tandemly repeated. Molecular cloning and sequence analysis revealed that the BamHI fragments are mainly composed of a family of closely related sequences that are 95 bp long (EEEo1, for Eliminated Element of E. okinoseanus 1), and the DraI fragment is composed of another family of closely related sequences that are 85 bp long (EEEo2). The two DNA families account for about 19% of the total eliminated DNA in E. okinoseanus type A. Fluorescence in situ hybridization experiments demonstrated that the two families of DNA are located on several C-band-positive, small chromosomes that are limited to germ cells in both types of E. okinoseanus.by W. Hennig     

Satellite DNA properties of the germ line limited DNA and the organization of the somatic genomes in the nematodesAscaris suum andParascaris equorum

During the early cleavage divisions in some Ascarids, parts of the chromosomes are eliminated from the somatic blastomeres (chromatin diminution, Boveri, 1887) while the chromosomes in the germ line cells maintain their integrity. To characterize the germ line and soma genome, DNA was isolated from gametes and embryonic somatic cells of two Ascarid species,Parascaris equorum var. univalens andAscaris suum. It was shown that the germ line limited DNAs of these species have the same density and almost identical reassociation kinetics: in CsCl the predominant component of the germ line limited DNA ofP. equorum andA. suum has the buoyant density of 1.697g/cm³, while soma DNA of both species bands at 1.700 g/cm³. InP. equorum there is a small additional germ line limited satellite DNA component with the density of 1.690 g/cm³, identical to that of mitochondrial DNA of both organisms. Comparison of the reassociation kinetics of germ line and soma DNA demonstrates for both species that the eliminated DNA sequences are highly repetitive. In contrast to these similarities between the germ line limited DNAs ofP. equorum andA. suum the analysis of their base composition revealed differences (40% guanine plus cytosine inP. equorum and 36% inA. suum). The only very fast reassociating DNA sequences which we could isolate from soma DNA was demonstrated to be foldback DNA. The reassociation kinetics of totalA. suum soma DNA was investigated by hydroxylapatite chromatography. Least squares analysis of the data revealed about 10% of intermediate repetitive DNA sequences. Their interspersion between single copy DNA sequences was analyzed by comparing the reassociation kinetics of DNA fragments 0.35 and 7.2 kilobases long. Thus the DNA sequence arrangement ofAscaris does not follow the short period interspersion pattern observed in most organism.     

Chromosome-specific alpha satellite DNA from human chromosome 1: hierarchical structure and genomic organization of a polymorphic domain spanning several hundred kilobase pairs of centromeric DNA

The human alpha satellite repetitive DNA family is organized as distinct chromosome-specific subsets localized to the centromeric region of each chromosome. Here, we report he isolation and characterization of cloned repeat units which define a hierarchical subset of alpha satellite on human chromosome 1. This subset is characterized by a 1.9-kb higher-order repeat unit which consists of 11 tandem approximately 171-bp alpha satellite monomer repeat units. The higher-order repeat unit is itself tandemly repeated, present in at least 100 copies at the centromeric region of chromosome 1. Using pulsed-field gel electrophoresis we estimate the total array length of these tandem sequences at the centromere of chromosome 1 to be several hundred kilobase pairs. Under conditions of high stringency, the higher-order repeat probe hybridizes specifically to chromosome 1 and can be used to detect several associated restriction fragment length DNA polymorphisms. As such, this probe may be useful for molecular and genetic analyses of the centromeric region of human chromosome 1.     

Identification of two families of satellite-like repetitive DNA sequences from the zebrafish (Brachydanio rerio).

To further our understanding of the structure and organization of the zebrafish genome, we have undertaken the analysis of highly and middle-repetitive DNA sequences. We have cloned and sequenced two families of tandemly repeated DNA fragments. The monomer units of the Type I satellite-like sequence are 186 bp long, A+T-rich (65%), and exhibit a high degree of sequence conservation. The Type I satellite-like sequence constitutes 8% of the zebrafish genome, or approximately 8 x 10(5) copies per haploid genome. Southern analysis of genomic DNA, digested with several restriction endonucleases, shows a ladder of hybridizing bands, consistent with a tandem array, and suggests longer range periodic variations in the sequence of the tandem repeats. The Type II satellite has a monomer length of 165 bp, is also A+T-rich (68%), and constitutes 0.2% of the zebrafish genome (22,000 copies per haploid genome). Southern analysis reveals a complex pattern rather than a ladder of regularly spaced hybridizing bands.     

PCR amplification of tandemly repeated DNA: analysis of intra- and interchromosomal sequence variation and homologous unequal crossing-over in human alpha satellite DNA.

Tandemly repeated DNA can comprise several percent of total genomic DNA in complex organisms and, in some instances, may play a role in chromosome structure or function. Alpha satellite DNA is the major family of tandemly repeated DNA found at the centromeres of all human and primate chromosomes. Each centromere is characterized by a large contiguous array of up to several thousand kb which can contain several thousand highly homogeneous repeat units. By using a novel application of the polymerase chain reaction (repPCR), we are able to amplify a representative sampling of multiple repetitive units simultaneously, allowing rapid analysis of chromosomal subsets. Direct sequence analysis of repPCR amplified alpha satellite from chromosomes 17 and X reveals positions of sequence heterogeneity as two bands at a single nucleotide position on a sequencing ladder. The use of TdT in the sequencing reactions greatly reduces the background associated with polymerase pauses and stops, allowing visualization of heterogeneous bases found in as little as 10% of the repeat units. Confirmation of these heterogeneous positions was obtained by comparison to the sequence of multiple individual cloned copies obtained both by PCR and non-PCR based methods. PCR amplification of alpha satellite can also reveal multiple repeat units which differ in size. Analysis of repPCR products from chromosome 17 and X allows rapid determination of the molecular basis of these repeat unit length variants, which appear to be a result of unequal crossing-over. The application of repPCR to the study of tandemly repeated DNA should allow in-depth analysis of intra- and interchromosomal variation and unequal crossing-over, thus providing insight into the biology and genetics of these large families of DNA.     

Isolation and chromosomal localization of a germ line-specific highly repetitive DNA family in Acricotopus lucidus (Diptera, Chironomidae)

. In the chironomid Acricotopus lucidus, parts of the genome, the germ line-limited chromosomes, are eliminated from the future soma cells during early cleavage divisions. A highly repetitive, germ line-specific DNA sequence family was isolated, cloned and sequenced. The monomers of the tandemly repeated sequences range in size from 175 to 184 bp. Analysis of sequence variation allowed the further classification of the germ line-restricted repetitive DNA into two related subfamilies, A and B. Fluorescence in situ hybridization to gonial metaphases demonstrated that the sequence family is highly specific for the paracentromeric heterochromatin of the germ line-limited chromosomes. Restriction analysis of genomic soma DNA of A. lucidus revealed another tandem repetitive DNA sequence family with monomers of about 175 bp in length. These DNA elements are found only in the centromeric regions of all soma chromosomes and one exceptional germ line-limited chromosome by in situ hybridization to polytene soma chromosomes and gonial metaphase chromosomes. The sequences described here may be involved in recognition, distinction and behavior of soma and germ line-limited chromosomes during the complex chromosome cycle in A. lucidus and may be useful for the genetic and cytological analysis of the processes of elimination of the germ line-limited chromosomes in the soma and germ line. Received: 12 April 1997; in revised form 26 June 1997 / Accepted: 29 June 1997