MAFG

Key takeaways

MAFG belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MAFG to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MAFG from memory before moving on to harder problems.

Reference excerpt

Transcription factor MafG is a bZip Maf transcription factor protein that in humans is encoded by the MAFG gene. MafG is one of the small Maf proteins, which are basic region and leucine zipper (bZIP)-type transcription factors. The HUGO Gene Nomenclature Committee-approved gene name of MAFG is “v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog G”.

Discovery MafG was first cloned and identified in chicken in 1995 as a new member of the small Maf (sMaf) genes. MAFG has been identified in many vertebrates, including humans. There are three functionally redundant sMaf proteins in vertebrates, MafF, MafG, and MafK.

Structure MafG has a bZIP structure that consists of a basic region for DNA binding and a leucine zipper structure for dimer formation. Similar to other sMafs, MafG lacks any canonical transcriptional activation domains.

Expression MAFG is broadly but differentially expressed in various tissues. MAFG expression was detected in all 16 tissues examined by the human BodyMap Project, but relatively abundant in lung, lymph node, skeletal muscle and thyroid tissues. MafG gene expression is induced by oxidative stresses, such as hydrogen peroxide and electrophilic compounds. Mouse Mafg gene is induced by Nrf2-sMaf heterodimers through an antioxidant response element (ARE) at the promoter proximal region. In response to bile acids, mouse Mafg gene is induced by the nuclear receptor, FXR (Farnesoid X receptor).

Function Because of sequence similarity, no functional differences have been observed among the sMafs in terms of their bZIP structures. sMafs form homodimers by themselves and heterodimers with other specific bZIP transcription factors, such as CNC (cap 'n' collar) proteins [p45 NF-E2 (NFE2), Nrf1 (NFE2L1), Nrf2 (NFE2L2), and Nrf3 (NFE2L3)] and Bach proteins (BACH1 and BACH2). sMaf homodimers bind to a palindromic DNA sequence called the Maf recognition element (MARE: TGCTGACTCAGCA) and its related sequences. Structural analyses have demonstrated that the basic region of a Maf factor recognizes the flanking GC sequences. By contrast, CNC-sMaf or Bach-sMaf heterodimers preferentially bind to DNA sequences (RTGA(C/G)NNNGC: R=A or G) that are slightly different from MARE. The latter DNA sequences have been recognized as antioxidant/electrophile response elements or NF-E2-binding motifs to which Nrf2-sMaf heterodimers and p45 NF-E2-sMaf heterodimer bind, respectively. It has been proposed that the latter sequences should be classified as CNC-sMaf-binding elements (CsMBEs). It has also been reported that sMafs form heterodimers with other bZIP transcription factors, such as c-Jun and c-Fos.

Target genes sMafs regulate different target genes depending on their partners. For instance, the p45-NF-E2-sMaf heterodimer regulate genes responsible for platelet production. Nrf2-sMaf heterodimer regulates a battery of cytoprotective genes, such as antioxidant/xenobiotic metabolizing enzyme genes. The Bach1-sMaf heterodimer regulates the heme oxygenase-1 gene. In particular, it has been reported that Bach1-MafG heterodimers participate in the hypermethylation of genes with CpG island promoters in certain types of cancers. The contribution of individual sMafs to the transcriptional regulation of their target genes has not yet been well examined.

Disease linkage Loss of sMafs results in disease-like phenotypes as summarized in table below. Mice lacking MafG exhibit mild neuronal phenotype and mild thrombocytopenia. However, mice lacking Mafg and one allele of Mafk (Mafg−/−::Mafk+/−) exhibit more severe neuronal phenotypes, severe thrombocytopenia and cataracts. Mice lacking MafG and MafK (Mafg−/−::Mafk−/− ) die in the perinatal stage. Finally, mice lacking MafF, MafG and MafK are embryonic lethal. Embryonic fibroblasts that are derived from Maff−/−::Mafg−/−::Mafk−/− mice fail to activate Nrf2-dependent cytoprotective genes in response to stress.

In addition, accumulating evidence suggests that as partners of CNC and Bach proteins, sMafs are involved in the onset and progression of various human diseases, including neurodegeneration, arteriosclerosis and cancer.

Notes

References

Illustrations

Worked examples

Example 1 — a first encounter with MAFG

Start with the simplest possible case. Write down what MAFG claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MAFG before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MAFG ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MAFG

In research: MAFG appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MAFG in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MAFG is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 17, Transcription factors, Wikipedia articles with corresponding academic peer reviewed articles, so understanding it makes those chapters shorter.
In everyday life: Look for MAFG outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study MAFG in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MAFG means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MAFG out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MAFG in simple terms?

Transcription factor MafG is a bZip Maf transcription factor protein that in humans is encoded by the MAFG gene. MafG is one of the small Maf proteins, which are basic region and leucine zipper (bZIP)-type transcription factors.

Why does MAFG matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MAFG?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MAFG.