Essential Bacillus subtilis genes

To estimate the minimal gene set required to sustain bacterial life in nutritious conditions, we carried out a systematic inactivation of Bacillus subtilis genes. Among approximately 4,100 genes of the organism, only 192 were shown to be indispensable by this or previous work. Another 79 genes were predicted to be essential. The vast majority of essential genes were categorized in relatively few domains of cell metabolism, with about half involved in information processing, one-fifth involved in the synthesis of cell envelope and the determination of cell shape and division, and one-tenth related to cell energetics. Only 4% of essential genes encode unknown functions. Most essential genes are present throughout a wide range of Bacteria, and almost 70% can also be found in Archaea and Eucarya. However, essential genes related to cell envelope, shape, division, and respiration tend to be lost from bacteria with small genomes. Unexpectedly, most genes involved in the Embden-Meyerhof-Parnas pathway are essential. Identification of unknown and unexpected essential genes opens research avenues to better understanding of processes that sustain bacterial life.

Relation between myocardial function and expression of sarcoplasmic reticulum Ca(2+)-ATPase in failing and nonfailing human myocardium

Expression of sarcoplasmic reticulum (SR) Ca(2+)-ATPase was shown to be reduced in failing human myocardium. The functional relevance of this finding, however, is not known. We investigated the relation between myocardial function and protein levels of SR Ca(2+)-ATPase in nonfailing human myocardium (8 muscle strips from 4 hearts) and in myocardium from end-stage failing hearts with dilated (10 muscle strips from 9 hearts) or ischemic (7 muscle strips from 5 hearts) cardiomyopathy. Myocardial function was evaluated by the force-frequency relation in isometrically contracting muscle strip preparations (37 degrees C, 30 to 180 min-1). In nonfailing myocardium, twitch tension rose with increasing rates of stimulation and was 76% higher at 120 min-1 compared with 30 min-1 (P < .02). In failing myocardium, there was no significant increase in average tension at stimulation rates above 30 min-1. At 120 min-1, twitch tension was decreased by 59% (P < .05) in dilated cardiomyopathy and 76% (P < .05) in ischemic cardiomyopathy compared with nonfailing myocardium. Protein levels of SR Ca(2+)-ATPase, normalized per total protein or per myosin, were reduced by 36% (P < .02) or 32% (P < .05), respectively, in failing compared with nonfailing myocardium. SR Ca(2+)-ATPase protein levels were closely related to SR Ca2+ uptake, measured in homogenates from the same hearts (r = .70, n = 16, and P < .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Gene expression of the cardiac Na(+)-Ca2+ exchanger in end-stage human heart failure

The regulation of cytosolic Ca2+ concentration during excitation-contraction coupling is altered in the failing human heart. Previous studies have focused on disturbances in Ca2+ release and reuptake from the sarcoplasmic reticulum (SR), whereas functional studies of the cardiac Na(+)-Ca2+ exchanger, another important determinant of myocyte homeostasis, are lacking for the failing human heart. Using a cardiac Na(+)-Ca2+ exchanger cDNA recently cloned from a guinea pig cDNA library, we investigated the gene expression of the cardiac Na(+)-Ca2+ exchanger in relation to the SR Ca(2+)-ATPase. Expression of both genes was quantified in left ventricular myocardium from 24 failing human cardiac explants and 7 control heart samples in relation to beta-myosin heavy chain mRNA by slot blot analysis. Compared with patients with nonfailing hearts, patients with dilated cardiomyopathy (DCM, n = 13) showed a 55% increase in Na(+)-Ca2+ exchanger mRNA levels (P < .05 versus control value) and a 41% increase in patients with coronary artery disease (CAD, n = 11). In the same hearts, SR Ca(2+)-ATPase mRNA levels were decreased by 50% in DCM and by 45% in CAD (P < .05 for both versus control value). There was a positive correlation between Na(+)-Ca2+ exchanger and SR Ca(2+)-ATPase mRNA levels both in normal and failing human hearts, albeit with different slopes and intercepts of the regression line. The Na(+)-Ca2+ exchanger protein levels as assessed by Western blot analysis and normalized to beta-myosin heavy chain protein were increased in DCM and CAD (P < .05 and P < .01 versus control value, respectively), whereas SR Ca(2+)-ATPase protein levels were reduced (P < .05 for both groups versus control values). Thus, the Na(+)-Ca2+ exchanger gene expression is enhanced in failing human hearts and may, in part, compensate for the depressed SR function with regard to diastolic Ca2+ removal.

A schizophrenia-related sensorimotor deficit links alpha 3-containing GABAA receptors to a dopamine hyperfunction

Overactivity of the dopaminergic system in the brain is considered to be a contributing factor to the development and symptomatology of schizophrenia. Therefore, the GABAergic control of dopamine functions was assessed by disrupting the gene encoding the alpha3 subunit of the GABA(A) receptor. alpha3 knockout (alpha3KO) mice exhibited neither an obvious developmental defect nor apparent morphological brain abnormalities, and there was no evidence for compensatory up-regulation of other major GABA(A)-receptor subunits. Anxiety-related behavior in the elevated-plus-maze test was undisturbed, and the anxiolytic-like effect of diazepam, which is mediated by alpha2-containing GABA(A) receptors, was preserved. As a result of the loss of alpha3 GABA(A) receptors, the GABA-induced whole-cell current recorded from midbrain dopamine neurons was significantly reduced. Spontaneous locomotor activity was slightly elevated in alpha3KO mice. Most notably, prepulse inhibition of the acoustic startle reflex was markedly attenuated in the alpha3KO mice, pointing to a deficit in sensorimotor information processing. This deficit was completely normalized by treatment with the antipsychotic D2-receptor antagonist haloperidol. The amphetamine-induced hyperlocomotion was not altered in alpha3KO mice compared with WT mice. These results suggest that the absence of alpha3-subunit-containing GABA(A) receptors induces a hyperdopaminergic phenotype, including a severe deficit in sensorimotor gating, a common feature among psychiatric conditions, including schizophrenia. Hence, agonists acting at alpha3-containing GABA(A) receptors may constitute an avenue for an effective treatment of sensorimotor-gating deficits in various psychiatric conditions.

Nitric oxide in osteoarthritis

Activated articular chondrocytes produce large amounts of nitric oxide (NO), and there is increasing evidence that this is involved in the etiopathogenesis of osteoarthritis (OA). Because of its short half-life, the biological effects of endogenously produced NO are likely to occur locally within the cartilage. We have observed that inhibitors of NO synthases relieve the inhibition of matrix synthesis that otherwise occurs in response to IL-1. To avoid the use of inhibitors, we have recently transduced chondrocytes with the iNOS (NOS-2) gene and confirmed the ability of the endogenously produced NO to inhibit matrix synthesis. Despite the high levels of NO made by these cells, there was no evidence of apoptosis or other forms of cell death. NO was also shown to inhibit the production of TGF-beta(1)by cells treated with IL-1, as well as to decrease matrix production in response to IGF-1. The hypothesis that NO inhibits matrix production by interfering with important autocrine and paracrine factors should be entertained.

Increased angiotensin-I converting enzyme gene expression in the failing human heart. Quantification by competitive RNA polymerase chain reaction

Local activation of the components of the renin angiotensin system in the heart is regarded as an important modulator of cardiac phenotype and function; however, little is known about their presence, regulation, and potential activation in the human heart. To investigate the gene expression of major angiotensin-II-forming enzymes in left ventricles of normal (n = 9) and failing human hearts (n = 20), we established a competitive RNA-polymerase chain reaction (PCR) for mRNA quantification of angiotensin-I converting enzyme (ACE) and human heart chymase. For each gene, competitor RNA targets with small internal deletions were used as internal standards to quantify the original number of transcripts and to control reverse transcription and PCR. In PCR, each target and the corresponding competitor were amplified by competing for the same primer oligonucleotides. The variability of ACE RNA-PCR was 11% indicating a high reproducibility of this method. In addition, ACE mRNA levels obtained by competitive RNA-PCR correlated favorably with traditional slot blot hybridization (r = 0.69, n = 10; P < 0.05). Compared with nonfailing hearts, the number of ACE transcripts referred to 100 ng of total RNA was increased threefold in patients with chronic heart failure (4.2 +/- 2.5 vs. 12.8 +/- 6 x 10(5); P < 0.0005). In contrast, no significant difference was found in chymase gene expression between normal and failing hearts. Thus, the expression of the cardiac ACE but not of human heart chymase is upregulated in failing human heart indicating an activation of the cardiac renin-angiotensin system in patients with advanced heart failure.

Expression, activity and functional significance of inducible nitric oxide synthase in the failing human heart

OBJECTIVES

The study was designed to evaluate the functional impact of nitric oxide (NO) generation within the myocardium on cardiac contraction in the failing human heart.

BACKGROUND

Heart failure is associated with activation of cytokines and expression of inducible nitric oxide synthase (NOS II), which generates NO from L-arginine. Nitric oxide has been shown to modulate myocardial performance, raising the possibility that cardiac generation of NO by NOS II modulates cardiac contraction in the failing human heart.

METHODS

Left ventricular (LV) tissue of 24 patients with end-stage heart failure was obtained during cardiac transplantation. Gene expression of NOS II and endothelial NO-synthase (NOS III) was quantified by competitive reverse transcription-polymerase chain reaction and compared to tissues of five nonfailing donor hearts. Nitric oxide synthase II activity was determined by citrulline assay and related to changes in force of contraction induced by the beta-adrenergic agonist isoproterenol, NO-donors and/or N-mono-methyl-L-arginine (L-NMMA), an inhibitor of NOS.

RESULTS

While NOS III mRNA was reduced in failing hearts, NOS II mRNA was increased in failing LV tissue and correlated with NOS II activity. High NOS II activity was associated with early relaxation and impaired responsiveness to beta-adrenergic stimulation, that is, the inotropic response to isoproterenol in failing hearts was inversely related to NOS II activity (r=0.61, p < 0.005). Nitric oxide donors or L-NMMA did not affect myocardial performance in failing hearts at baseline. However, L-NMMA enhanced the positive inotropic response to beta-adrenergic stimulation in failing hearts with high NOS II activity. Nitric oxide donors attenuated the isoproterenol-induced increase in force of contraction of failing hearts.

CONCLUSIONS

Cardiac production of NO by NOS II attenuates the positive inotropic effects of beta-adrenergic stimulation and hastens relaxation in failing human hearts.

Increased expression of endothelial constitutive nitric oxide synthase in rat aorta during pregnancy

The mechanisms underlying enhanced vascular reactivity in pregnancy are not yet defined. In this study we have investigated the potential role of endothelium-derived vasodilator nitric oxide (EDNO). EDNO-mediated dilatory responses in vitro were markedly increased in aorta of pregnant as compared with nonpregnant rats. This increase in EDNO-releasability was accompanied by a two-fold increase in mRNA of endothelial constitutive nitric oxide synthase (NOS-III). Chronically substituted estrogen, but neither progesterone nor testosterone induced an upregulation of NOS-III mRNA in aorta of gonadectomized rats which amounted to about half that induced in aorta of pregnant rats. Thus, increased EDNO-releasability and increased NOS-III mRNA contribute to enhanced vascular reactivity in pregnancy.

Survival after myocardial infarction in the rat. Role of tissue angiotensin-converting enzyme inhibition

BACKGROUND

Chronic treatment with high doses of angiotensin-converting enzyme (ACE) inhibitors prolongs survival after myocardial infarction. Since the plasma renin-angiotensin system (RAS) is not consistently activated in the chronic phase after myocardial infarction, the beneficial effects of ACE inhibition have been attributed, in part, to inhibition of an activated tissue RAS. However, a relation between tissue ACE inhibition and long-term efficacy (ie, concerning left ventricular [LV] hypertrophy and survival) has not been established. The present study was designed to evaluate the impact of low-dose ACE inhibition (predominant inhibition of plasma ACE) and high-dose ACE inhibition associated with substantial tissue ACE inhibition) on reversal of LV hypertrophy and 1-year mortality after myocardial infarction in the rat.

METHODS AND RESULTS

Infarcted rats were randomized to placebo, low-dose lisinopril, or high-dose lisinopril (each, n = 80) and compared with sham-operated animals (n = 40). In a separate group of animals, tissue ACE activity was determined after 6 weeks of therapy, demonstrating that both regimens were effective with regard to both plasma and pulmonary ACE inhibition; however, only high-dose lisinopril inhibited renal ACE. Neither dose affected LV ACE activity and ACE mRNA levels as determined by competitive polymerase chain reaction, whereas LV ANF mRNA levels were significantly reduced by high-dose lisinopril. High-dose lisinopril reduced arterial blood pressure and normalized right ventricular and LV weight and resulted in a substantial reduction of 1-year mortality, whereas the low dose did not (1 year mortality: placebo, 56.3%; low dose, 53.3%; high dose, 22.9%, P < .0001 versus low dose and versus placebo).

CONCLUSIONS

Hemodynamically effective ACE inhibition is required for reduction of LV hypertrophy and long-term mortality after myocardial infarction in the rat. Sustained inhibition of renal ACE during long-term therapy may contribute to the beneficial effect of high-dose lisinopril. Low-dose lisinopril, although exerting sustained inhibition of the plasma ACE, does not improve survival after myocardial infarction.

Location of the genes controlling H-Y antigen expression and testis determination on the mouse Y chromosome

Sex-reversed XX male mice that carry the variant form of the testis-determining Sxr region, Sxr', do not express male-specific H-Y antigen. In a stock of mice segregating for Sxr', we detected an exceptional XX male that proved positive for H-Y antigen. DNA fingerprinting revealed that the banding pattern characteristic of Sxr' had been replaced by the pattern associated with the native testis-determining region of the normal Y chromosome of that stock, presumably by pairing and crossing-over between the two testis-determining regions of the father's Y Sxr' chromosome. Pairing between the two ends of such a chromosome in a loop-like configuration has been observed by electron microscopy. However, an anomalous crossing-over event of this kind would only give rise to the observed result if the native homologue of the Sxr region were situated on the very minute short arm of the Y chromosome. We therefore conclude that the two linked genes Tdy and Hya, controlling testis determination and H-Y antigen expression, respectively, are located on the short arm of the mouse Y chromosome.

Reciprocal changes in the postnatal expression of the sarcolemmal Na+-Ca(2+)-exchanger and SERCA2 in rat heart

The aim of this study was to examine the relationship between sarcolemmal Na(+)-Ca2+ exchangers and sarcoplasmic reticulum (SR) Ca(2+) -ATPase (SERCA2) expression and the developmental differences in cardiac Ca2+ handling. Postnatal steady-state mRNA and protein levels were analysed in rat ventricular myocardium by Northern and immunoblot analysis, respectively. This was compared to Na+ gradient-induced and SR oxalate-supported Ca2 transport in isolated membranes. Na(+)-Ca2+ exchanger mRNA declined by 75% between day 1 and 30, whereas SR Ca2+ ATPase mRNA levels increased by 97% during this period. The Na(+)-Ca2+ exchanger mRNA/Ca(2+)-ATPase mRNA ratio was found to be inversely related to post-natal age. The changes in mRNA levels were associated with corresponding developmental differences in the Ca2+ transport activities of the respective membrane proteins. In crude membranes, the Na(+)-dependent Ca2+ transport activity (at 75 microM Ca2+) declined gradually (P < 0.01; mean +/- S.E.) from 17.7 +/- 2.4 nmoles Ca2+/g wet tissue/2s at day 1-3 (n = 5) to a value of 4.2 +/- 1.1 at day 40 (n =4). Conversely, SR Ca2+ uptake increased (P < 0.01) 2.6-fold during this period. The inversely related changes in the post-natal expression and function of the Na(+)-Ca2+ exchanger and SR Ca(2+)-ATPase suggest a coordinated control at the pretranslational level of the cellular Ca2+ transport processes mediated by the two membrane proteins.

Calcium cycling proteins and force-frequency relationship in heart failure

Myocardial function, intracellular calcium and levels of calcium cycling proteins were analyzed in failing and nonfailing human myocardium. Myocardial function was evaluated by the isometric force-frequency relation, and intracellular calcium was studied by aequorin light emission. When stimulation frequency was increased above 30 min-1, there was a continuous increase in isometric tension development in the nonfailing myocardium. In contrast, in failing myocardium, frequency potentiation of contractile force was blunted or inverse. As a consequence, at higher rates of stimulation, twitch tension was reduced significantly in failing compared to nonfailing human myocardium. Aequorin measurements indicated that the contractile deficit in the failing myocardium at higher rates of stimulation is associated with decreased free intracellular calcium concentration. Western blot analysis indicated that in the failing myocardium protein levels of SR-Ca(2+)- ATPase are significantly reduced and protein levels of Na(+)-Ca(2+)- exchanger are significantly increased. Levels of phospholamban are slightly reduced in the failing myocardium, and ryanodine receptor and calsequestrin protein levels are unchanged. There was a close positive correlation between the protein levels of SR-Ca(2+)-ATPase and frequency potentiation of contractile force. From these data, we conclude that in failing compared to nonfailing human myocardium 1) force-frequency relation is blunted or inverse. 2) Frequency-dependence of contractile force is closely correlated with frequency-dependence of intracellular calcium cycling. 3) Protein levels of SR-Ca(2+)-ATPase may determine frequency-dependence of sarcoplasmic reticulum calcium release. 4) Calcium elimination by an increased number of Na(+)-Ca2-exchanger molecules may be a compensatory mechanism to prevent diastolic calcium accumulation in failing myocardium with a reduced number of SR calcium pumps.

Differential effects of kinins on cardiomyocyte hypertrophy and interstitial collagen matrix in the surviving myocardium after myocardial infarction in the rat

BACKGROUND

Left ventricular remodeling after myocardial infarction (MI) involves the hypertrophic growth of cardiomyocytes and the accumulation of fibrillar collagen in the interstitial space. We evaluated the role of kinins in postinfarction ventricular remodeling and their potential contribution to the antiremodeling effects of ACE inhibition and angiotensin II type 1 (AT1) receptor blockade.

METHODS AND RESULTS

Rats underwent coronary artery ligation followed by chronic B2 kinin receptor blockade with icatibant. Additional groups of infarcted rats were treated with the ACE inhibitor lisinopril or the AT1 receptor antagonist ZD7155, each separately and in combination with icatibant. B2 kinin receptor blockade enhanced the interstitial deposition of collagen after MI, whereas morphological and molecular markers of cardiomyocyte hypertrophy (cardiac weight, myocyte cross-sectional area, prepro-atrial natriuretic factor mRNA expression) were not affected. Chronic ACE inhibition and AT1 receptor blockade reduced collagen deposition and cardiomyocyte hypertrophy after MI. The inhibitory action of ACE inhibition and AT1 receptor blockade on interstitial collagen was partially reversed by B2 kinin receptor blockade. However, B2 kinin receptor blockade did not attenuate the effects of ACE inhibition and AT1 receptor blockade on cardiomyocyte hypertrophy.

CONCLUSIONS

(1) Kinins inhibit the interstitial accumulation of collagen but do not modulate cardiomyocyte hypertrophy after MI. (2) Kinins contribute to the reduction of myocardial collagen accumulation by ACE inhibition and AT1 receptor blockade. (3) The effects of ACE inhibition and AT1 receptor blockade on cardiomyocyte hypertrophy are related to a reduced generation/receptor blockade of angiotensin II.

Effects of calcium ionophores on the transport and distribution of calcium in isolated cells and in liver and kidney slices

The effects of calcium ionophores on cellular calcium metabolism were studied in cultured kidney cells, in cells freshly isolated from rat kidney, and in liver and kidney slices. In isolated cells, these ionophores decreased the total cellular Ca content and the mitochondrial Ca. 45Ca efflux from prelabelled cells was also stimulated even in the absence of extracellular Ca. In slices, the ionphore A23187 increased the total slice Ca and the uptake of 45Ca. However, the mitochondria isolated from these slices treated with the ionophore had a lower total Ca and a depressed relative radioactivity. These results suggest that the increased cytosolic Ca produced by Ca ionophores may be due to mobilization of intracellular Ca stores rather than to a net shift of Ca from the extracellular fluids to the cell.

Expression and function of the cardiac Na+/Ca2+ exchanger in postnatal development of the rat, in experimental-induced cardiac hypertrophy and in the failing human heart

The diastolic and systolic dysfunction in the failing heart appear to be related to the altered Ca2+ handling of the cardiac myocyte. Disturbed Ca2+ handling might also affect influx and efflux of other ions, including Na+. In this context, the cardiac sarcolemmal Na+/Ca2+ exchanger represents an important exchange mechanism of Ca2+ versus Na+ transport across the sarcolemma. Expression and function of cardiac Na+/Ca2+ exchanger is highest in newborn rats and declines gradually in postnatal development. In pressure overload-induced hypertrophy, expression of cardiac Na+/Ca2+ exchanger is increased and translated into increased Na+/Ca2+ exchanger activity similar to the early phase of postnatal development in the rat. This suggests a common underlying mechanism in the control of Na+/ Ca2+ exchanger expression in the immature and the hypertrophied myocardium. Similar to experimental-induced hypertrophy, mRNA, protein and activity of Na+/ Ca2+ exchanger is increased in the failing human heart suggesting an increase in the number of functional exchanger molecules rather than an enhanced exchange rate by preexisting exchanger molecules. The potential functional implications of an increased cardiac Na+/Ca2+ exchanger activity in human heart failure may be limitation of diastolic intracellular Ca2+ overload. However, this may increase the arrhythmogenic potential of the failing heart, since additional Na+ influx via Na+/Ca2+ exchanger may affect the membrane potential.

Simple GATCA repeats characterize the X chromosomal heterochromatin of Microtus agrestis, European field vole (Rodentia, Cricetidae)

The sex chromosomes of Microtus agrestis are extremely large due to the accumulation of constitutive heterochromatin. We have identified two prominent satellite bands of 2.0 and 2.8 kb in length after HaeIII and HinfI restriction enzyme digestion of genomic DNA, respectively. These satellites are located on the heterochromatic long arm of the X chromosome as shown using Microtus x mouse somatic cell hybrids. By in-gel hybridization with oligonucleotide probes, the organization of the two satellites was studied: among the many copies of the simple tandem tetranucleotide repeat GATA are interspersed rare single GACA tetramers. One of the satellites also harbours related GGAT simple tandem repeats. In situ hybridizations with plasmid-carried or oligonucleotide GATCA probes show clustered silver grains on the long and short arm of the X chromosome. Interspersion of differently organized (GATA)n elements is also demonstrable in the autosomal complement and on the Y chromosome. These results are discussed in the context of the evolution of vertebrate sex chromosomes in relation to heterochromatin and simple repetitive DNA sequences.

Metallothionein accretion in human hepatic cells is linked to cellular proliferation

The basal amounts of metallothionein (MT) and its rates of biosynthesis were compared in resting and proliferating Chang liver (CCl-13) cells. In resting cells the total amounts of the detectable isoforms MT-2 and MT-1e were approx. 1.6x10(6) and 4x10(5) molecules per cell respectively. In exponentially growing cultures the cellular contents of both isoforms increased co-ordinately approx. 4-fold and decreased again to the initial values within 48 h after entering density-mediated growth arrest. As documented for MT-2 its transient accretion was attributable to a 10-fold rise in the rate of biosynthesis of this protein during the growth phase. Measurements of the relative amounts of MT-2 mRNA indicated the occurrence of a more than 50% increase within the first 12 h after subculturing of the cells, followed by a return to basal levels thereafter. These results denote a direct link between the programming of MT synthesis and proliferation and thus attest to a central housekeeping function of the MTs.

Dissecting (CAC)5/(GTG)5 multilocus fingerprints from man into individual locus-specific, hypervariable components

Individual components of multilocus fingerprints from man produced by (CAC)5/(GTG)5 oligonucleotides have been scrutinized to characterize their peculiar properties. Successful cloning and changes occurring during the propagation of recombinant simple repetitive DNA in prokaryotic hosts are described. The isolated locus-specific probes were characterized with respect to their formal (and population genetic) properties and their usefulness for individualization and linkage studies. The localization was determined on chromosomes 8, 9, 11, and 22. Repeat flanking sequences were characterized and analyzed for their coding potential because of significant open reading frames and apparent evolutionary conservation among vertebrates. The organization of the repeats and their flanking regions in the human genome is discussed with respect to the sequence (fine) architecture that developed during evolution. Classical "minisatellite" sequences were not detected near hypervariable (cac)n/(gtg)n repeats. The single-copy probes described herein are a convenient complement to the oligonucleotides employed for multilocus fingerprinting. Many practical applications are apparent.

Organization of DYZ2 repetitive DNA on the human Y chromosome

The location of the human Y-specific repetitive DNA sequence DYZ2 with HaeIII cleavage sites spaced at 2.1 kb was reexamined. Previous reports had mapped the 2000 DYZ2 copies to the very distal end of the heterochromatic Yq12 band. In the present study, a cloned DYZ2 fragment (pHY2.1) was used for Southern and slot blot analyses of male DNA as well as for nonradioactive in situ hybridization to chromosomes. DNA and metaphase preparations from 79 individuals with polymorphic or aberrant Y chromosomes were examined. DYZ2 repeats are not confined to the distal tip of Yq12, but extend through the entire heterochromatin of Yq12. In the naturally occurring length polymorphisms of Yq, the amount of DYZ2 sequence varies in proportion to the measured sizes of band Yq12. Explanations are presented for the fact that previous studies restricted the location of DYZ2 to the telomeric end of Yq12.