Here the 2.1 Å crystal structure of human immunodeficiency virus (HIV) Tat protein complexed with the positive transcription elongation factor P-TEFb is reported. This shows that Tat binding changes the structure of P-TEFb, which may suggest opportunities for developing inhibitors that block only the form of P-TEFb used by the virus.

Electromagnetically induced transparency enables the transmission of a laser pulse through an optically dense medium to be manipulated using a control beam. Here this technique is scaled down to a single atom, which acts as a quantum-optical transistor with the ability to coherently control the transmission of light through a cavity. This may lead to novel quantum applications, such as dynamic control of the photon statistics of propagating light fields.

Attosecond (10?18 s) laser pulses make it possible to peer into the inner workings of atoms and molecules on the electronic timescale — phenomena in solids have already been investigated in this way. Here, an attosecond pump–probe experiment is reported that investigates the ionization and dissociation of hydrogen molecules, illustrating that attosecond techniques can also help explore the prompt charge redistribution and charge localization that accompany photoexcitation processes in molecular systems.