The present invention relates to a cell which has been modified in comparison with its wild type in such a way that it is capable of forming more, by comparison with its wild, 3-hydroxyisobutyric acid or poly-hydroxyalkanoates based on 3-hydroxyisobutyric acid via methylmalonate-semialdehyde or 3-hydroxybutyryl-coenzyme A as precursors. The invention also relates to a method of generating a genetically modified cell, to the genetically modified cell obtainable by these methods, to a method of producing 3-hydroxyisobutyric acid or polyhydroxyalkanoates based on 3-hydroxyisobutyric acid, to a method of producing methacrylic acid or methacrylic esters, and to a method of producing polymethacrylic acid or polymethacrylic esters. The present invention furthermore 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.