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#assay

3 public questions tagged with this topic.

Transcript analysis

In a DNase I footprinting assay, a missing band indicates:

DNase I footprinting identifies precise binding sites of DNA-binding proteins. End-labeled DNA fragment is partially digested with DNase I, a non-specific endonuclease introducing single-strand nicks at random phosphodiester bonds, generating ladder when resolved on denaturing gel. Pre-incubation with DNA-binding protein protects phosphodiester backbone within contact region from cleavage, preventing production of corresponding fragments. Hence protected region appears as gap, or missing bands, footprint against background ladder. Position of gap defines recognition site, while flanking cleavage pattern provides sequence context for transcription factor binding analysis.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Transcript analysis

EMSA detects:

Electrophoretic Mobility Shift Assay is a classic in vitro technique for studying nucleic acid-protein interactions. A radiolabeled or fluorescent double-stranded DNA fragment containing putative protein binding motif is incubated with nuclear extract or purified protein. If specific binding protein recognizes sequence, formation of protein-DNA complex increases molecular mass and reduces net negative charge, causing retardation during non-denaturing polyacrylamide gel electrophoresis compared to free probe. The assay can also detect protein-protein interactions via supershift when additional partner increases complex size. It does not measure protein degradation or folding status directly.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

Which assay uses a solid-phase microarray?

Protein microarray is a high-throughput platform where hundreds to thousands of purified proteins, antibodies, or peptides are immobilized in defined spots on functionalized glass slide or nitrocellulose membrane. This solid-phase array enables parallel analysis of protein expression, post-translational modifications, and interaction networks from minimal sample volume. Detection uses fluorescence, chemiluminescence, or SPR imaging. Western blot separates proteins electrophoretically, co-immunoprecipitation isolates complexes in solution, and PAGE is purely separative. Microarray format provides multiplexing advantage for proteome-wide screening and biomarker discovery under controlled conditions.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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