DNA system provided the first clear suggestion that DNA carries genetic information. In 1933, while studying virgin sea urchin eggs, Jean Brachet suggested that DNA is found in the cell nucleus and that RNA is present exclusively in the cytoplasm. At the time, "yeast nucleic acid" (RNA) was thought to occur only in plants, while "thymus nucleic acid" (DNA) only in animals. The latter was thought to be a tetramer, with the function of buffering cellular pH. In 1937, William Astbury produced the first X-ray diffraction patterns that showed that DNA had a regular structure. In 1943, Oswald Avery, along with
DNA methylation in cancer lung cancers or non-small-cell lung cancer squamous cell carcinomas. The article Werner syndrome ATP-dependent helicase indicates the DNA repair gene "WRN" has a promoter that is frequently hypermethylated in a number of cancers, with hypermethylation occurring in 11% to 38% of colorectal, head and neck, stomach, prostate, breast, thyroid, non-Hodgkin lymphoma, chondrosarcoma and osteosarcoma cancers (see WRN). As discussed by Jin and Roberston in their review, silencing of a DNA repair gene by hypermethylation may be a very early step in progression to cancer. Such silencing is proposed to act similarly to a germ-line mutation in a DNA repair gene,