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
Transfer DNA Transfer DNA The transfer DNA (abbreviated T-DNA) is the transferred DNA of the tumor-inducing (Ti) plasmid of some species of bacteria such as "Agrobacterium tumefaciens" and "[[Agrobacterium rhizogenes](actually an Ri plasmid)]". The T-DNA is transferred from bacterium into the host plant's [[cell nucleus|nuclear]] DNA [[genome]]. The capability of this specialized tumor-inducing (Ti) plasmid is attributed to two essential regions required for DNA transfer to the host cell. As the T-DNA is bordered by 25-base-pair repeats on each end. Transfer is initiated at the right border and terminated at the left border and requires the "vir" genes of the Ti plasmid.