Methoxyamine attack on cytosine produces ambivalent base pairing properties of the modified base.

We report the solution structure of two heptanucleotides each containing a central N4-methoxycytosine, in one case with adenine on the opposite strand and in the other with guanine. For the N4-methoxycytosine-adenine pair only the imino form of the N4-methoxycytosine residue is observed and base pairing is in Watson-Crick geometry. However, rotation of the methoxy group about the N-OCH3 bond is not constrained to a particular orientation although it must be anti to the N3 of N4-methoxycytosine. The slow exchange on a proton NMR time scale between the single strand and double strand forms is attributed to the strong preference of the syn conformation of the OCH3 group in the single strand which inhibits base pair formation. For N4-methoxycytosine base paired with guanosine we observe the N4-methoxycytosine base in the amino form in Watson-Crick geometry and a slow exchange of this species with an imino form base paired in wobble geometry. The amino form is predominant at low temperature whereas the imino form predominates above 40 degrees C. Our results point to preferential replacement of dTTP by N4-methoxycytosine in primer elongation.

Nitrogen Compounds Transported in the Xylem of Sugar Cane

Microcapillary tubes were inserted directly into xylem vessels of leaves and stalks of sugar cane (Saccharum spp.) to determine the form in which nitrogen is translocated from the roots towards the leaves. On a low nitrogen regime, the xylem fluid of both sugar cane and related species and genera contained nitrogen dominantly in the amino form. Nitrate was also present and increased markedly in some varieties when the supply of nitrate fertilizer to the roots was increased. The amino N and nitrate N levels tended to be lowest in the xylem fluid of those leaves most active in photosynthesis.

SCFMO Study of the Tautomerism of Anilino-Thiazole and Related Compounds

SCFMO study of the tautomerism of anilino-thiazole, anilino-oxazole, and anilino-oxadiazole shows that amino form predominates.