MI-3

MI-3 is an inhibitor of Menin-Mixed linage leukemia (MML) protein interaction with IC50 value of 648 ± 25 nM [1].

MLL protein is a histone methyltransferase that positively regulates gene transcription. However, MLL gene is a common target for chromosomal translocations found in some leukemia. Fusion of MLL gene with one of over 50 different partner genes forms chimeric oncogenes encoding MLL fusion proteins. Translocations will disrupt the regulatory ability of MLL protein on HOX gene, resulting in enhanced cell proliferation and blocked hematopoietic differentiation. Menin is a tumor suppressor protein which directly controls cell growth in endocrine organs. Importantly, menin is also a highly specific partner of MLL. The regulatory function of MLL and MLL fusion protein is facilitated by the association of menin. Therefore, the interaction between MLL fusion protein and menin is critical for the pathology of leukemia [1].

In HEK293 cells expressing menin and MLL-AF9 fusion protein, treatment of MI-3 resulted in significant disruption of menin-MLL-AF9 complex without affecting expression level of menin and MLL-AF9 complex [1]. In mouse bone marrow cells (BMC) transduced with MLL-AF9 and MLL-ENL, MI-3 was observed to effectively inhibit menin-MLL interaction-induced cell proliferation, transformation and hematopoietic differentiation [1].

In human MLL leukemia cell lines harboring different translocations, MI-3 treatment showed an effective and dose-dependent growth inhibition of several cell lines with different MLL translocations [1].

Reference:
[1] Grembecka J et al. , Menin-MLL inhibitors reverse oncogenic activity of MLL fusion proteins in leukemia. Nature Chemical Biology. 2012, 8(3): 277-284.

A missense mutation in the oxi-3 gene of the [mi-3] extranuclear mutant of Neurospora crassa.[Pubmed:3007516]

J Biol Chem. 1986 Apr 25;261(12):5610-5.

We have determined the DNA sequence of the oxi-3 gene and its 5' flanking region in the extranuclear [MI-3] mutant of Neurospora crassa. The oxi-3 gene encodes subunit 1 of cytochrome c oxidase, a protein known to be altered in the [MI-3] mutant (Bertrand, H., and Werner, S. (1979) Eur. J. Biochem. 98, 9-18). When the sequence from [MI-3] was compared to previously published sequences of the same region of mtDNA from wild-type N. crassa, a total of five differences was found. Four of these differences can be accounted for as either genetic polymorphisms or previous errors in DNA sequence determination. The remaining difference is a G/C to T/A transversion that changes a codon specifying an aspartic acid residue (GAC) to one that would specify tyrosine (TAC) at amino acid 448 of the 555 amino acid mature subunit 1 protein. This alteration was also found in the mtDNA of two separate heterokaryotic strains that had acquired the [MI-3] phenotype after repeated subculturing of heterokaryons forced between an [MI-3] strain and a strain containing a wild-type cytoplasm. The particular aspartic acid residue that would be affected by the mutation observed in [MI-3] is conserved in a diversity of species as either aspartic acid or glutamic acid, suggesting that an acidic residue at this position is important for the correct function of the subunit 1 protein. For these reasons, we consider it likely that the observed missense mutation is responsible for the [MI-3] phenotype.

Conversion of a mitochondrial precursor polypeptide into subunit 1 of cytochrome oxidase in the mi-3 mutant of Neurospora crassa.[Pubmed:227683]

Eur J Biochem. 1979 Sep;99(3):463-70.

1. The cytochrome-alpha alpha 3-deficient MI-3 cytoplasmic mutant of Neurospora crassa synthesizes a mitochondrial translation product which crossreacts with antibodies specific to subunit 1 of cytochrome oxidase. The immunoprecipitated polypeptide migrates more slowly during gel electrophoresis than the authentic 41 000-Mr subunit 1 of the wild-type enzyme. An apparent molecular weight of about 45 000 was estimated for the mutant product. 2. Radioactive labelling experiments in vivo show that the crossreacting material found in the mutant is relatively stable and does not form complexes with other subunits of the oxidase. 3. After induction of a functional cytochrome oxidase in the mutant cells with antimycin A, the 45 000-Mr polypeptide is converted to a 41 000-Mr component, which exhibits the same electrophoretic mobility as subunit 1 of the oxidase. Pulse-chase labelling kinetics reveal a typical precursor product relationship. 4. The converted polypeptide becomes assembled with other enzyme subunits to form a protein complex which has the immunological characteristics of cytochrome oxidase. A possible physiological role of the post-translational processing of the mitochondrially synthesized component is discussed.

Fine mapping of the nematode resistance gene Mi-3 in Solanum peruvianum and construction of a S. lycopersicum DNA contig spanning the locus.[Pubmed:16021467]

Mol Genet Genomics. 2005 Aug;274(1):60-9.

Currently, the only genetic resistance against root-knot nematodes in the cultivated tomato Solanum lycopersicum (Lycopersicon esculentum) is due to the gene Mi-1. Another resistance gene, MI-3, identified in the related wild species Solanum peruvianum (Lycopersicon peruvianum) confers resistance to nematodes that are virulent on tomato lines that carry Mi-1, and is effective at temperatures at which Mi-1 is not effective (above 30 degrees C). Two S. peruvianum populations segregating for MI-3 were used to develop a high-resolution map of the MI-3 region of chromosome 12. S. lycopersicum BACs carrying flanking markers were identified and used to construct a contig spanning the MI-3 region. Markers generated from BAC-end sequences were mapped in S. peruvianum plants in which recombination events had occurred near MI-3. Comparison of the S. peruvianum genetic map with the physical map of S. lycopersicum indicated that marker order is conserved between S. lycopersicum and S. peruvianum. The 600 kb contig between MI-3-flanking markers TG180 and NR18 corresponds to a genetic distance of about 7.2 cM in S. peruvianum. We have identified a marker that completely cosegregates with MI-3, as well as flanking markers within 0.25 cM of the gene. These markers can be used to introduce MI-3 into cultivated tomato, either by conventional breeding or cloning strategies.

Behavior of the [mi-3] mutation and conversion of polymorphic mtDNA markers in heterokaryons of Neurospora crassa.[Pubmed:1977658]

Genetics. 1990 Sep;126(1):63-72.

We have examined the behavior of the [MI-3] mitochondrial mutation and two physical mtDNA markers in heterokaryotic cultures of Neurospora crassa. Previous workers showed that a 1.2-kilobase insertion in the larger polymorphic form of EcoRI-5 restriction fragment is a site of high frequency and rapid unidirectional gene conversion. We have confirmed this observation and determined by DNA sequence analysis that the insertion in the EcoRI-5 fragment corresponds precisely to an optional intron that contains a long open reading frame in the ND1 gene. Thus, the conversion of the short, intron-lacking, form of EcoRI-5 to the longer, intron-containing, form may be analogous to the unidirectional gene conversion events catalyzed by intron-encoded proteins in other organisms. The resolution of two polymorphic forms of the mtDNA EcoRI-9 restriction fragment in our heterokaryons differs from that observed previously and suggests that this locus is not a site of gene conversion in our heterokaryon pair. The size polymorphism of the EcoRI-9 fragments is due to a tandemly reiterated 78-base-pair sequence which occurs two times in the short form and three times in the long form. One copy of the repeat unit and 66 base pairs following it have been duplicated from the ND2 gene which is located about 30 kilobases distant on the mtDNA. In contrast to the [poky] mitochondrial mutant, which was completely dominant over wild-type mitochondria in heterokaryons, the [MI-3] mutant was recovered in only seven of twenty heterokaryons after ten cycles of conidiation and subculturing. The resolution of the [MI-3] or wild-type phenotype in heterokaryons may depend solely on random factors such as allele input frequency, drift, and segregation rather than specific dominant or suppressive effects.