The role of a repetitive DNA motif (5'-CAAT-3') in the variable expression of the Haemophilus influenzae lipopolysaccharide epitope ?Gal(1?4)?Gal

The locus lex2, comprising lex2A and lex2B, contributes to the phase-variable expression of lipopolysaccharide (LPS) of Haemophilus influenzae and was found to be present in 74 % of strains investigated. lex2A contains 5′-GCAA repeats which vary in number from 4 to 46 copies between strains. The locus was cloned from the serotype b strains RM7004 and RM153 and showed >99 % nucleotide sequence identity between these strains and the published lex2 sequence. Disruption of the lex2B gene in strain RM7004 resulted in truncation of some LPS glycoforms, shown by gel fractionation, with only one glycoform reacting with a digalactoside-specific monoclonal antibody, 4C4, compared with four LPS glycoforms in the more elongated LPS of the parent strain. Mass spectrometry and NMR analyses of LPS from the lex2B mutant revealed loss of the terminal digalactoside as well as the second β-glucose extending from the first heptose of the inner core. The authors conclude that Lex2B is the β-(1-4)-glucosyltransferase that adds the second β-glucose to the first β-glucose as part of the oligosaccharide extension from the first heptose of the LPS of strain RM7004. Investigation of the expression of the lex2 locus indicated that the genes are co-transcribed and that both reading frames are required for addition of this second β-glucose in a phase-variable manner.

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Role of CCAA Nucleotide Repeats in Regulation of Hemoglobin and Hemoglobin-Haptoglobin Binding Protein Genes ofHaemophilus influenzae

Journal of Bacteriology ◽

10.1128/jb.181.18.5865-5870.1999 ◽

1999 ◽

Vol 181 (18) ◽

pp. 5865-5870 ◽

Cited By ~ 38

Author(s):

Zhen Ren ◽

Hongfan Jin ◽

Paul W. Whitby ◽

Daniel J. Morton ◽

Terrence L. Stull

Keyword(s):

Haemophilus Influenzae ◽

Gene Fusion ◽

Binding Protein ◽

Phase Variable ◽

Repeat Region ◽

Variable Expression ◽

Ofhaemophilus Influenzae ◽

Nucleotide Repeats

ABSTRACT Haemophilus influenzae utilizes hemoglobin and hemoglobin-haptoglobin as heme sources. The H. influenzaehemoglobin- and hemoglobin-haptoglobin binding protein genes,hgpA, hgpB, and hgpC, contain lengths of tetrameric CCAA repeats. Using an hgpA-lacZtranslational gene fusion, we demonstrate phase-variable expression oflacZ associated with alteration in the length of the CCAA repeat region.

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DNA methylation in satellite repeats disorders

Essays in Biochemistry ◽

10.1042/ebc20190028 ◽

2019 ◽

Vol 63 (6) ◽

pp. 757-771 ◽

Cited By ~ 4

Author(s):

Claire Francastel ◽

Frédérique Magdinier

Keyword(s):

Dna Methylation ◽

Human Genome ◽

Repetitive Dna ◽

Dna Sequences ◽

Satellite Repeats ◽

Tremendous Progress ◽

Genes Encoding ◽

Dna Elements ◽

Near Future

Abstract Despite the tremendous progress made in recent years in assembling the human genome, tandemly repeated DNA elements remain poorly characterized. These sequences account for the vast majority of methylated sites in the human genome and their methylated state is necessary for this repetitive DNA to function properly and to maintain genome integrity. Furthermore, recent advances highlight the emerging role of these sequences in regulating the functions of the human genome and its variability during evolution, among individuals, or in disease susceptibility. In addition, a number of inherited rare diseases are directly linked to the alteration of some of these repetitive DNA sequences, either through changes in the organization or size of the tandem repeat arrays or through mutations in genes encoding chromatin modifiers involved in the epigenetic regulation of these elements. Although largely overlooked so far in the functional annotation of the human genome, satellite elements play key roles in its architectural and topological organization. This includes functions as boundary elements delimitating functional domains or assembly of repressive nuclear compartments, with local or distal impact on gene expression. Thus, the consideration of satellite repeats organization and their associated epigenetic landmarks, including DNA methylation (DNAme), will become unavoidable in the near future to fully decipher human phenotypes and associated diseases.

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A Certain Future: Epistemicity, Prediction, and Assertion in Iberian Spanish Future Expression

Studies in Hispanic and Lusophone Linguistics ◽

10.1515/shll-2014-1166 ◽

2014 ◽

Vol 7 (2) ◽

Cited By ~ 1

Author(s):

Jessi E. Aaron

Keyword(s):

Quantitative Methods ◽

Epistemic Modality ◽

Romance Languages ◽

Variable Expression ◽

Distributional Patterns ◽

Periphrastic Future ◽

Synthetic Construction ◽

Future Reference

AbstractThe choice of future construction in Romance languages with variable expression is complex, and several factors have been shown or hypothesized to influence this choice (e.g. Aaron 2006, 2010 and Poplack & Malvar 2007). One factor stands out time and time again, though scholars do not always associate it with the same form: certainty. Using corpus-based quantitative methods, the role of certainty in Iberian Spanish future form variation is examined. The semantics of futurity and epistemic modality are discussed, with particular reference to the Spanish synthetic, or morphological, future. Then, the onset of non-future-reference use of the Synthetic Future as an epistemic marker is described, and viewed in light of the role of epistemicity in the possible strengthening of the semantics of “certainty” with the Spanish Periphrastic Future. Finally, diachronic evidence from distributional patterns in grammatical person, verb class and clause type is presented, which suggests that speakers associate the periphrastic construction with “certainty” and, increasingly, the synthetic construction with “uncertainty.” It is suggested that functional competition with innovative forms can breathe new life into older forms, sparking further grammaticalization.

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Elucidation of the Monoclonal Antibody 5G8-Reactive, Virulence-Associated Lipopolysaccharide Epitope of Haemophilus influenzae and Its Role in Bacterial Resistance to Complement-Mediated Killing

Infection and Immunity ◽

10.1128/iai.73.4.2213-2221.2005 ◽

2005 ◽

Vol 73 (4) ◽

pp. 2213-2221 ◽

Cited By ~ 11

Author(s):

Ruth Griffin ◽

Andrew D. Cox ◽

Katherine Makepeace ◽

James C. Richards ◽

E. Richard Moxon ◽

...

Keyword(s):

Monoclonal Antibody ◽

Haemophilus Influenzae ◽

Bacterial Resistance ◽

Inner Core ◽

Phase Variation ◽

Phase Variable ◽

Type B ◽

Variable Expression ◽

Virulent Type ◽

Unknown Structure

ABSTRACT The phase-variable locus lex2 is required for expression of a Haemophilus influenzae lipopolysaccharide (LPS) epitope of previously unknown structure. This epitope, which is reactive with monoclonal antibody (MAb) 5G8, has been associated with virulence of type b strains. When strain RM118 (from the same source as strain Rd), in which the lex2 locus and MAb 5G8 reactivity are absent, was transformed with lex2 DNA, transformants that were reactive with MAb 5G8 were obtained. Surprisingly, the 5G8 reactivity of these transformants was phase variable, although the lex2 locus lacked tetrameric repeats and was constitutively expressed. This phase variation was shown to be the result of phase-variable expression of phosphorylcholine (PCho) such that MAb 5G8 reacted only in the absence of PCho. Structural analysis showed that, compared to RM118, the lex2 transformant had acquired a tetrasaccharide, Gal-α1,4-Gal-β1,4-Glc-β1,4-Glc-β1,4, linked to the proximal heptose (HepI). A terminal GalNAc was detected in a minority of glycoforms. LPS derived from a mutant of RM7004, a virulent type b strain which naturally expresses lex2 and has LPS containing the same tetrasaccharide linked to HepI as the sole oligosaccharide extension from the inner core, confirmed that GalNAc is not a part of the MAb 5G8-reactive epitope. Thus, MAb 5G8 specifically binds to the structure Gal-α1,4-Gal-β1,4-Glc-β1,4-Glc-β attached via a 1,4 linkage to HepI of H. influenzae LPS, and we show that the ability to synthesize this novel tetrasaccharide was associated with enhanced bacterial resistance to complement-mediated killing.

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