The present invention relates to a cell which has been genetically modified by comparison with its wild type in such a way that it is able to form more, by comparison with its wild type, 3-hydroxyisobutyric acid or polyhydroxyalkanoates based on 3-hydroxyisobutyric acid via methylmalonate semialdehyde or 3-hydroxybutyryl-coenzyme A as precursors. The invention also relates to a method for producing a genetically modified cell, to the genetically modified cell obtainable by this method, to a method for producing 3-hydroxyisobutyric acid or polyhydroxyalkanoates based on 3-hydroxyisobutyric acid, to a method for producing methacrylic acid or methacrylic esters, and to a method for producing polymethacrylic acid or polymethacrylic esters. The present invention further relates to an isolated DNA, to a vector, to the use of this vector for transforming a cell, to a transformed cell, and to a polypeptide.