First runner-up: RNA ascending. RNA molecules, long viewed as little more than couriers shuttling messages or amino acids around the cell, are turning out to be remarkably versatile. Small pieces of RNA are known to shut down genes in the nematode Caenorhabditis elegans, a phenomenon very similar to gene silencing, which occurs in plants. RNA interference (RNAi) could be a boon to studies of gene function (ScienceNOW, 23 May), so interest in RNA has exploded. This year, molecular biologists discovered that RNAi can quell gene activity in mouse and human cells as well.
Meanwhile, others learned more about the production of the more familiar messenger RNA (mRNA): High-resolution pictures captured the yeast RNA polymerase II--which builds the mRNA based on the gene's sequence--in action, and researchers found key proteins involved in splicing together the coding regions of mRNA after non-coding sequence has been removed.
Researchers also made an important discovery about the spliceosome, the complex of proteins and RNAs that removes noncoding sequence from nascent mRNA. They found that the spliceosome's RNAs, not its proteins, control the removal of unwanted sequence. This has spawned a new field, "ribozymology," aimed at clarifying and harnessing RNA's enzymatic potential. In one experiment, researchers forced RNA enzymes or "ribozymes" to evolve by selecting for those that are able to replicate RNA. These results indicate that RNA could have preceded DNA in the earliest life-forms (ScienceNOW, 17 May).
Neutrino mystery solved. One of the great triumphs of science in the past century has been understanding how stars burn nuclear fuel. But physicists have always been puzzled by the fact that an expected byproduct--so-called "electron" neutrinos--were not nearly as abundant as required by the straightforward theory. In 1998, one group presented evidence that seemed to explain the discrepancy: They had shown that neutrinos "oscillate" from one flavor (such as the electron neutrino) to another (such as the muon or tau neutrino). If the electron neutrinos were turning into another variety as they streamed away from the sun, that would explain the shortfall of electron neutrinos. In June, scientists at the Sudbury Neutrino Observatory in Ontario announced results showing that this is indeed is the case (ScienceNOW, 18 June).
Neutrino Observatory Suffers Accident (ScienceNOW, 13 November)
Undiscovered Particle or Fluke? (ScienceNOW, 12 November)
The Latest Angle on Neutrinos (ScienceNOW, 31 October)
Proposed Lab a Scientific Gold Mine (ScienceNOW, 13 June)
Turning the Moon Into a Particle Detector (ScienceNOW, 9 May)
Buried South Pole Scope Spots Neutrinos (ScienceNOW, 23 March)
Genomes take off. This year, two competing international teams published the landmark drafts of the 3.3 billion base pair sequence that defines our species (ScienceNOW, 12 February). The big surprise when the drafts were revealed: Our genetic code contains only about 35,000 genes, not even twice as many as the lowly worm, Caenorhabditis elegans. (By year's end, however, the number began creeping upward.)
Sequences of more than 60 other organisms are done. Most are those are microbes, such as Staphylococcus (ScienceNOW, 20 April) and other human pathogens. A draft sequence of the Japanese puffer fish genome--the most compact genome of all vertebrates--is now in the public databases (ScienceNOW, 26 October). The sequencing of the rat (ScienceNOW, 5 March), mouse, zebrafish, a freshwater puffer fish, a malaria mosquito (ScienceNOW, 6 March), the fungus Neurospora crassa, and fission yeast is proceeding at full speed. Similarly, private companies announced that they have rough copies of the rice and mouse genome sequences (ScienceNOW, 27 April).
Chimp Sequencing Wins Commitments (ScienceNOW, 19 March)
New S. pneumoniae Genome Published (ScienceNOW, 20 July)
Miniature Genome Sequenced (ScienceNOW, 26 April)
Pneumonia Genome Yields Vaccine Targets (ScienceNOW, 14 March)
Banana Genome Eyed (ScienceNOW, 19 July)
Gut Microbes' Genomes Unveiled (ScienceNOW, 24 October)
Ancient Genomes Sequenced (ScienceNOW, 7 February)
Bad Hamburger Bug Sequenced (ScienceNOW, 24 January)
Superconductor surprises. Two teams discovered vastly different superconductors at higher than expected temperatures. Early in the year, researchers announced that one of the simplest compounds in the chemistry stockroom--magnesium diboride--becomes a superconductor at 39 Kelvin (ScienceNOW, 16 February). The second surprising superconductor is made of C60 molecules, popularly called buckyballs. In August, researchers announced that when they stuffed organic molecules into a crystal of C60, the distance between the buckyballs increased and the superconductivity temperature rocketed to 117 K (ScienceNOW, 30 August). The researchers hope to hike that further to room temperature, opening new possibilities for superconducting molecular electronics.
A Superconductor Breaks the Mold (ScienceNOW, 13 December)
Guide me home. Several studies over the past year helped sort out the controls that help neural projections called axons find their way during embryo development. One study showed that, when presented with conflicting signals (one stop and one go), the growing tip of an axon doesn't get confused. Additional studies this year focused on how the message received at the axon's surface translates into axon movement. It turns out that the signals activate regulators that instruct the actin cytoskeleton to build up the axon in one direction or another.
Climatic confidence. A major milestone was reached in January when the United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC) officially declared that "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations" (ScienceNOW, 22 January). A better understanding of climate change finally allowed IPCC to pin much of the blame for rising temperatures on human activities. It has become clear that even a combination of volcanic debris, solar flickering, and the natural jostlings of the climate system could not explain the 0.6°C warming of the past century.
Cancer in the crosshairs. Thirty years after President Richard Nixon and the U.S. Congress declared a "War on Cancer," a new breed of cancer drugs is entering the clinic. This year, the U.S. Food and Drug Administration (FDA) approved a drug called Gleevec for use in treating one kind of leukemia. It's a milestone because Gleevec is the first small-molecule drug that works by targeting the specific biochemical defect that causes the cancer. (But see ScienceNOW, 21 June.)
Banner year for Bose-Einstein. Cooled atoms that march in quantum lockstep were big news in 1995, and this year that work garnered physics Nobel honors for their discoverers (ScienceNOW, 9 October). But the field hasn't rested on its laurels. In March, two groups figured out how to make Bose-Einstein condensates (BECs) of so-called metastable helium, a result that might lead to laserlike beams of atoms that could carve nanocircuits out of silicon. Scientists also acquired new skills in manipulating the condensates. They observed a kind of atomic supernova, dubbed a "bose nova," in a BEC, as part of the atomic vapor collapsed on itself, throwing off a miniature shock wave of atoms akin to the blast from a collapsing star.
Carbon consensus. Researchers who had been puzzling over how much carbon dioxide is absorbed by U.S. forests and fields have finally reconciled their conflicting results. The consensus is about 500 million metric tons, or about one-third of current U.S. emissions. Researchers now hope a similar approach will pinpoint carbon uptake in other regions, such as the tropics, where it seems to fluctuate most. The bad news: Because much of the U.S. sink is due to ecosystems recovering from past exploitation, this sponge is steadily shrinking and will taper off within 100 years.
--The NEWS and EDITORIAL STAFFS
An expanded version of the Breakthrough of the Year section, with references and links, is posted at Science Online